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	$12.67	7.137%	$13.5743	$13.57	$13.55	$13.60
Purchase #2	$223.89	4.771%	$234.5718	$234.57	$234.55	$234.60
Purchase #3	$210.29	8.545%	$228.2593	$228.26	$228.25	$228.30
Purchase #4	$53.51	3.543%	$55.4059	$55.41	$55.40	$55.40
Purchase #5	$36.42	10.569%	$40.2692	$40.27	$40.25	$40.30
Purchase #6	$78.82	11.528%	$87.9064	$87.91	$87.90	$87.90
Purchase #7	$154.86	13.352%	$175.5369	$175.54	$175.55	$175.50
7 purchase totals =	$770.46		$835.5238	$835.53	$835.45	$835.60