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	$248.91	3.190%	$256.8502	$256.85	$256.85	$256.90
Purchase #2	$223.59	7.535%	$240.4375	$240.44	$240.45	$240.40
Purchase #3	$18.28	13.287%	$20.7089	$20.71	$20.70	$20.70
Purchase #4	$97.63	10.744%	$108.1194	$108.12	$108.10	$108.10
Purchase #5	$247.35	3.702%	$256.5069	$256.51	$256.50	$256.50
Purchase #6	$60.30	9.156%	$65.8211	$65.82	$65.80	$65.80
Purchase #7	$88.48	8.246%	$95.7761	$95.78	$95.80	$95.80
7 purchase totals =	$984.54		$1,044.2201	$1,044.23	$1,044.20	$1,044.20