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	$145.39	6.722%	$155.1631	$155.16	$155.15	$155.20
Purchase #2	$108.49	10.374%	$119.7448	$119.74	$119.75	$119.70
Purchase #3	$34.89	7.443%	$37.4869	$37.49	$37.50	$37.50
Purchase #4	$229.78	3.700%	$238.2819	$238.28	$238.30	$238.30
Purchase #5	$232.71	13.749%	$264.7053	$264.71	$264.70	$264.70
Purchase #6	$244.90	3.329%	$253.0527	$253.05	$253.05	$253.10
Purchase #7	$164.33	3.516%	$170.1078	$170.11	$170.10	$170.10
7 purchase totals =	$1,160.49		$1,238.5425	$1,238.54	$1,238.55	$1,238.60