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	$229.94	9.238%	$251.1819	$251.18	$251.20	$251.20
Purchase #2	$200.38	4.593%	$209.5835	$209.58	$209.60	$209.60
Purchase #3	$166.34	8.362%	$180.2494	$180.25	$180.25	$180.20
Purchase #4	$116.49	10.319%	$128.5106	$128.51	$128.50	$128.50
Purchase #5	$134.82	13.612%	$153.1717	$153.17	$153.15	$153.20
Purchase #6	$125.71	8.835%	$136.8165	$136.82	$136.80	$136.80
Purchase #7	$123.89	10.634%	$137.0645	$137.06	$137.05	$137.10
7 purchase totals =	$1,097.57		$1,196.5781	$1,196.57	$1,196.55	$1,196.60