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	$248.72	9.593%	$272.5797	$272.58	$272.60	$272.60
Purchase #2	$159.98	7.859%	$172.5528	$172.55	$172.55	$172.60
Purchase #3	$219.79	10.676%	$243.2548	$243.25	$243.25	$243.30
Purchase #4	$161.91	6.303%	$172.1152	$172.12	$172.10	$172.10
Purchase #5	$56.60	5.268%	$59.5817	$59.58	$59.60	$59.60
Purchase #6	$50.33	3.213%	$51.9471	$51.95	$51.95	$51.90
Purchase #7	$163.28	9.778%	$179.2455	$179.25	$179.25	$179.20
7 purchase totals =	$1,060.61		$1,151.2768	$1,151.28	$1,151.30	$1,151.30