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	$47.50	7.116%	$50.8801	$50.88	$50.90	$50.90
Purchase #2	$59.40	8.360%	$64.3658	$64.37	$64.35	$64.40
Purchase #3	$42.53	7.650%	$45.7835	$45.78	$45.80	$45.80
Purchase #4	$100.55	11.699%	$112.3133	$112.31	$112.30	$112.30
Purchase #5	$103.88	7.419%	$111.5869	$111.59	$111.60	$111.60
Purchase #6	$20.25	12.421%	$22.7653	$22.77	$22.75	$22.80
Purchase #7	$140.29	9.162%	$153.1434	$153.14	$153.15	$153.10
7 purchase totals =	$514.40		$560.8383	$560.84	$560.85	$560.90