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	$55.48	10.766%	$61.453	$61.45	$61.45	$61.50
Purchase #2	$210.88	5.635%	$222.7631	$222.76	$222.75	$222.80
Purchase #3	$122.66	6.384%	$130.4906	$130.49	$130.50	$130.50
Purchase #4	$224.44	11.794%	$250.9105	$250.91	$250.90	$250.90
Purchase #5	$76.47	6.575%	$81.4979	$81.50	$81.50	$81.50
Purchase #6	$46.32	7.502%	$49.7949	$49.79	$49.80	$49.80
Purchase #7	$29.75	13.505%	$33.7677	$33.77	$33.75	$33.80
7 purchase totals =	$766.00		$830.6777	$830.67	$830.65	$830.80