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	$41.92	11.172%	$46.6033	$46.60	$46.60	$46.60
Purchase #2	$38.73	5.648%	$40.9175	$40.92	$40.90	$40.90
Purchase #3	$175.82	13.627%	$199.779	$199.78	$199.80	$199.80
Purchase #4	$180.86	4.836%	$189.6064	$189.61	$189.60	$189.60
Purchase #5	$193.37	8.354%	$209.5241	$209.52	$209.50	$209.50
Purchase #6	$130.75	5.634%	$138.1165	$138.12	$138.10	$138.10
Purchase #7	$11.45	12.832%	$12.9193	$12.92	$12.90	$12.90
7 purchase totals =	$772.90		$837.4661	$837.47	$837.40	$837.40