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	$138.29	6.619%	$147.4434	$147.44	$147.45	$147.40
Purchase #2	$89.30	3.145%	$92.1085	$92.11	$92.10	$92.10
Purchase #3	$57.94	6.291%	$61.585	$61.59	$61.60	$61.60
Purchase #4	$210.72	10.493%	$232.8308	$232.83	$232.85	$232.80
Purchase #5	$18.25	10.479%	$20.1624	$20.16	$20.15	$20.20
Purchase #6	$41.30	10.165%	$45.4981	$45.50	$45.50	$45.50
Purchase #7	$243.96	11.466%	$271.9325	$271.93	$271.95	$271.90
7 purchase totals =	$799.76		$871.5607	$871.56	$871.60	$871.50