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	$243.88	3.424%	$252.2305	$252.23	$252.25	$252.20
Purchase #2	$89.76	12.326%	$100.8238	$100.82	$100.80	$100.80
Purchase #3	$69.72	10.700%	$77.18	$77.18	$77.20	$77.20
Purchase #4	$104.38	13.851%	$118.8377	$118.84	$118.85	$118.80
Purchase #5	$122.32	6.569%	$130.3552	$130.36	$130.35	$130.40
Purchase #6	$135.49	5.464%	$142.8932	$142.89	$142.90	$142.90
Purchase #7	$32.27	4.634%	$33.7654	$33.77	$33.75	$33.80
7 purchase totals =	$797.82		$856.0858	$856.09	$856.10	$856.10