Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$105.85	9.481%	$115.8856	$115.89	$115.90	$115.90
Purchase #2	$201.49	10.288%	$222.2193	$222.22	$222.20	$222.20
Purchase #3	$147.92	4.712%	$154.89	$154.89	$154.90	$154.90
Purchase #4	$243.74	6.399%	$259.3369	$259.34	$259.35	$259.30
Purchase #5	$71.63	4.749%	$75.0317	$75.03	$75.05	$75.00
Purchase #6	$133.45	10.111%	$146.9431	$146.94	$146.95	$146.90
Purchase #7	$30.48	3.830%	$31.6474	$31.65	$31.65	$31.60
7 purchase totals =	$934.56		$1,005.9540	$1,005.96	$1,006.00	$1,005.80