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	$18.66	11.140%	$20.7387	$20.74	$20.75	$20.70
Purchase #2	$88.64	13.499%	$100.6055	$100.61	$100.60	$100.60
Purchase #3	$95.95	13.488%	$108.8917	$108.89	$108.90	$108.90
Purchase #4	$221.79	12.300%	$249.0702	$249.07	$249.05	$249.10
Purchase #5	$155.83	6.740%	$166.3329	$166.33	$166.35	$166.30
Purchase #6	$118.45	10.426%	$130.7996	$130.80	$130.80	$130.80
Purchase #7	$127.73	13.167%	$144.5482	$144.55	$144.55	$144.50
7 purchase totals =	$827.05		$920.9868	$920.99	$921.00	$920.90