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	$71.88	7.408%	$77.2049	$77.20	$77.20	$77.20
Purchase #2	$39.31	3.550%	$40.7055	$40.71	$40.70	$40.70
Purchase #3	$179.51	9.554%	$196.6604	$196.66	$196.65	$196.70
Purchase #4	$132.33	5.660%	$139.8199	$139.82	$139.80	$139.80
Purchase #5	$84.39	6.832%	$90.1555	$90.16	$90.15	$90.20
Purchase #6	$14.53	7.755%	$15.6568	$15.66	$15.65	$15.70
Purchase #7	$211.41	5.703%	$223.4667	$223.47	$223.45	$223.50
7 purchase totals =	$733.36		$783.6697	$783.68	$783.60	$783.80