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	$242.54	13.501%	$275.2853	$275.29	$275.30	$275.30
Purchase #2	$249.78	10.604%	$276.2667	$276.27	$276.25	$276.30
Purchase #3	$29.81	13.568%	$33.8546	$33.85	$33.85	$33.90
Purchase #4	$247.79	3.444%	$256.3239	$256.32	$256.30	$256.30
Purchase #5	$197.49	13.735%	$224.6153	$224.62	$224.60	$224.60
Purchase #6	$28.30	10.112%	$31.1617	$31.16	$31.15	$31.20
Purchase #7	$204.89	10.457%	$226.3153	$226.32	$226.30	$226.30
7 purchase totals =	$1,200.60		$1,323.8228	$1,323.83	$1,323.75	$1,323.90