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	$105.44	3.861%	$109.511	$109.51	$109.50	$109.50
Purchase #2	$83.70	7.760%	$90.1951	$90.20	$90.20	$90.20
Purchase #3	$94.76	5.628%	$100.0931	$100.09	$100.10	$100.10
Purchase #4	$61.70	4.313%	$64.3611	$64.36	$64.35	$64.40
Purchase #5	$99.27	4.168%	$103.4076	$103.41	$103.40	$103.40
Purchase #6	$85.89	5.108%	$90.2773	$90.28	$90.30	$90.30
Purchase #7	$203.55	11.700%	$227.3654	$227.37	$227.35	$227.40
7 purchase totals =	$734.31		$785.2106	$785.22	$785.20	$785.30