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	$225.69	6.398%	$240.1296	$240.13	$240.15	$240.10
Purchase #2	$72.38	8.183%	$78.3029	$78.30	$78.30	$78.30
Purchase #3	$47.30	12.856%	$53.3809	$53.38	$53.40	$53.40
Purchase #4	$250.48	13.130%	$283.368	$283.37	$283.35	$283.40
Purchase #5	$10.56	8.634%	$11.4718	$11.47	$11.45	$11.50
Purchase #6	$38.71	11.402%	$43.1237	$43.12	$43.10	$43.10
Purchase #7	$140.45	9.694%	$154.0652	$154.07	$154.05	$154.10
7 purchase totals =	$785.57		$863.8421	$863.84	$863.80	$863.90