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	$224.61	13.406%	$254.7212	$254.72	$254.70	$254.70
Purchase #2	$244.34	10.465%	$269.9102	$269.91	$269.90	$269.90
Purchase #3	$121.43	13.518%	$137.8449	$137.84	$137.85	$137.80
Purchase #4	$190.66	4.158%	$198.5876	$198.59	$198.60	$198.60
Purchase #5	$21.71	12.612%	$24.4481	$24.45	$24.45	$24.40
Purchase #6	$172.36	4.760%	$180.5643	$180.56	$180.55	$180.60
Purchase #7	$233.61	6.418%	$248.6031	$248.60	$248.60	$248.60
7 purchase totals =	$1,208.72		$1,314.6794	$1,314.67	$1,314.65	$1,314.60