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	$187.62	9.523%	$205.4871	$205.49	$205.50	$205.50
Purchase #2	$91.67	8.179%	$99.1677	$99.17	$99.15	$99.20
Purchase #3	$39.55	13.712%	$44.9731	$44.97	$44.95	$45.00
Purchase #4	$153.70	3.552%	$159.1594	$159.16	$159.15	$159.20
Purchase #5	$82.94	3.114%	$85.5228	$85.52	$85.50	$85.50
Purchase #6	$101.71	9.700%	$111.5759	$111.58	$111.60	$111.60
Purchase #7	$198.41	11.370%	$220.9692	$220.97	$220.95	$221.00
7 purchase totals =	$855.60		$926.8552	$926.86	$926.80	$927.00