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	$135.67	7.482%	$145.8208	$145.82	$145.80	$145.80
Purchase #2	$89.40	11.740%	$99.8956	$99.90	$99.90	$99.90
Purchase #3	$223.51	10.741%	$247.5172	$247.52	$247.50	$247.50
Purchase #4	$60.58	3.178%	$62.5052	$62.51	$62.50	$62.50
Purchase #5	$110.91	8.285%	$120.0989	$120.10	$120.10	$120.10
Purchase #6	$107.76	11.219%	$119.8496	$119.85	$119.85	$119.80
Purchase #7	$121.51	13.421%	$137.8179	$137.82	$137.80	$137.80
7 purchase totals =	$849.34		$933.5052	$933.52	$933.45	$933.40