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	$110.56	6.568%	$117.8216	$117.82	$117.80	$117.80
Purchase #2	$137.37	12.330%	$154.3077	$154.31	$154.30	$154.30
Purchase #3	$30.79	12.130%	$34.5248	$34.52	$34.50	$34.50
Purchase #4	$82.41	10.307%	$90.904	$90.90	$90.90	$90.90
Purchase #5	$37.31	9.673%	$40.919	$40.92	$40.90	$40.90
Purchase #6	$214.82	7.502%	$230.9358	$230.94	$230.95	$230.90
Purchase #7	$209.36	12.143%	$234.7826	$234.78	$234.80	$234.80
7 purchase totals =	$822.62		$904.1955	$904.19	$904.15	$904.10