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	$67.45	5.463%	$71.1348	$71.13	$71.15	$71.10
Purchase #2	$237.76	13.512%	$269.8861	$269.89	$269.90	$269.90
Purchase #3	$243.68	9.756%	$267.4534	$267.45	$267.45	$267.50
Purchase #4	$84.68	8.398%	$91.7914	$91.79	$91.80	$91.80
Purchase #5	$201.60	3.426%	$208.5068	$208.51	$208.50	$208.50
Purchase #6	$221.43	13.290%	$250.858	$250.86	$250.85	$250.90
Purchase #7	$128.88	8.588%	$139.9482	$139.95	$139.95	$139.90
7 purchase totals =	$1,185.48		$1,299.5787	$1,299.58	$1,299.60	$1,299.60