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	$99.52	11.696%	$111.1599	$111.16	$111.15	$111.20
Purchase #2	$70.84	7.433%	$76.1055	$76.11	$76.10	$76.10
Purchase #3	$55.68	4.667%	$58.2786	$58.28	$58.30	$58.30
Purchase #4	$42.58	11.461%	$47.4601	$47.46	$47.45	$47.50
Purchase #5	$174.54	5.534%	$184.199	$184.20	$184.20	$184.20
Purchase #6	$99.74	12.148%	$111.8564	$111.86	$111.85	$111.90
Purchase #7	$37.85	6.565%	$40.3349	$40.33	$40.35	$40.30
7 purchase totals =	$580.75		$629.3944	$629.40	$629.40	$629.50