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	$6.83	10.472%	$7.5452	$7.55	$7.55	$7.50
Purchase #2	$74.93	5.809%	$79.2827	$79.28	$79.30	$79.30
Purchase #3	$32.53	11.630%	$36.3132	$36.31	$36.30	$36.30
Purchase #4	$107.85	5.238%	$113.4992	$113.50	$113.50	$113.50
Purchase #5	$94.89	4.472%	$99.1335	$99.13	$99.15	$99.10
Purchase #6	$239.91	5.848%	$253.9399	$253.94	$253.95	$253.90
Purchase #7	$36.33	13.644%	$41.2869	$41.29	$41.30	$41.30
7 purchase totals =	$593.27		$631.0006	$631.00	$631.05	$630.90