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	$9.60	9.531%	$10.515	$10.52	$10.50	$10.50
Purchase #2	$189.55	11.397%	$211.153	$211.15	$211.15	$211.20
Purchase #3	$44.67	7.800%	$48.1543	$48.15	$48.15	$48.20
Purchase #4	$39.95	13.563%	$45.3684	$45.37	$45.35	$45.40
Purchase #5	$206.69	3.193%	$213.2896	$213.29	$213.30	$213.30
Purchase #6	$75.46	10.564%	$83.4316	$83.43	$83.45	$83.40
Purchase #7	$174.39	13.865%	$198.5692	$198.57	$198.55	$198.60
7 purchase totals =	$740.31		$810.4811	$810.48	$810.45	$810.60