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	$7.40	3.186%	$7.6358	$7.64	$7.65	$7.60
Purchase #2	$116.80	5.634%	$123.3805	$123.38	$123.40	$123.40
Purchase #3	$83.34	6.519%	$88.7729	$88.77	$88.75	$88.80
Purchase #4	$55.51	11.593%	$61.9453	$61.95	$61.95	$61.90
Purchase #5	$179.53	10.683%	$198.7092	$198.71	$198.70	$198.70
Purchase #6	$111.84	11.216%	$124.384	$124.38	$124.40	$124.40
Purchase #7	$61.39	8.724%	$66.7457	$66.75	$66.75	$66.70
7 purchase totals =	$615.81		$671.5734	$671.58	$671.60	$671.50