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	$185.76	9.562%	$203.5224	$203.52	$203.50	$203.50
Purchase #2	$52.81	8.723%	$57.4166	$57.42	$57.40	$57.40
Purchase #3	$87.43	9.674%	$95.888	$95.89	$95.90	$95.90
Purchase #4	$147.60	5.121%	$155.1586	$155.16	$155.15	$155.20
Purchase #5	$108.90	13.227%	$123.3042	$123.30	$123.30	$123.30
Purchase #6	$96.57	7.490%	$103.8031	$103.80	$103.80	$103.80
Purchase #7	$84.33	7.137%	$90.3486	$90.35	$90.35	$90.30
7 purchase totals =	$763.40		$829.4415	$829.44	$829.40	$829.40