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	$75.63	11.353%	$84.2163	$84.22	$84.20	$84.20
Purchase #2	$102.96	8.142%	$111.343	$111.34	$111.35	$111.30
Purchase #3	$12.45	9.525%	$13.6359	$13.64	$13.65	$13.60
Purchase #4	$59.67	12.832%	$67.3269	$67.33	$67.35	$67.30
Purchase #5	$55.34	5.336%	$58.2929	$58.29	$58.30	$58.30
Purchase #6	$127.33	7.227%	$136.5321	$136.53	$136.55	$136.50
Purchase #7	$58.69	4.773%	$61.4913	$61.49	$61.50	$61.50
7 purchase totals =	$492.07		$532.8384	$532.84	$532.90	$532.70