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	$250.65	13.118%	$283.5303	$283.53	$283.55	$283.50
Purchase #2	$120.82	13.805%	$137.4992	$137.50	$137.50	$137.50
Purchase #3	$213.94	3.174%	$220.7305	$220.73	$220.75	$220.70
Purchase #4	$159.89	12.374%	$179.6748	$179.67	$179.65	$179.70
Purchase #5	$80.73	9.630%	$88.5043	$88.50	$88.50	$88.50
Purchase #6	$31.31	6.541%	$33.358	$33.36	$33.35	$33.40
Purchase #7	$173.73	3.500%	$179.8106	$179.81	$179.80	$179.80
7 purchase totals =	$1,031.07		$1,123.1077	$1,123.10	$1,123.10	$1,123.10