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	$23.55	5.759%	$24.9062	$24.91	$24.90	$24.90
Purchase #2	$184.67	6.476%	$196.6292	$196.63	$196.65	$196.60
Purchase #3	$79.87	3.329%	$82.5289	$82.53	$82.55	$82.50
Purchase #4	$67.93	7.206%	$72.825	$72.83	$72.85	$72.80
Purchase #5	$150.44	13.166%	$170.2469	$170.25	$170.25	$170.20
Purchase #6	$187.91	11.853%	$210.183	$210.18	$210.20	$210.20
Purchase #7	$78.65	9.208%	$85.8921	$85.89	$85.90	$85.90
7 purchase totals =	$773.02		$843.2113	$843.22	$843.30	$843.10