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	$116.88	6.495%	$124.4714	$124.47	$124.45	$124.50
Purchase #2	$111.45	13.331%	$126.3074	$126.31	$126.30	$126.30
Purchase #3	$24.96	9.477%	$27.3255	$27.33	$27.35	$27.30
Purchase #4	$100.96	5.508%	$106.5209	$106.52	$106.50	$106.50
Purchase #5	$26.83	5.502%	$28.3062	$28.31	$28.30	$28.30
Purchase #6	$26.48	11.308%	$29.4744	$29.47	$29.45	$29.50
Purchase #7	$229.42	5.262%	$241.4921	$241.49	$241.50	$241.50
7 purchase totals =	$636.98		$683.8979	$683.90	$683.85	$683.90