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	$205.84	8.537%	$223.4126	$223.41	$223.40	$223.40
Purchase #2	$37.70	7.636%	$40.5788	$40.58	$40.60	$40.60
Purchase #3	$59.92	11.741%	$66.9552	$66.96	$66.95	$67.00
Purchase #4	$209.27	5.221%	$220.196	$220.20	$220.20	$220.20
Purchase #5	$178.65	5.273%	$188.0702	$188.07	$188.05	$188.10
Purchase #6	$32.90	7.373%	$35.3257	$35.33	$35.35	$35.30
Purchase #7	$172.75	13.801%	$196.5912	$196.59	$196.60	$196.60
7 purchase totals =	$897.03		$971.1297	$971.14	$971.15	$971.20