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	$191.61	4.224%	$199.7036	$199.70	$199.70	$199.70
Purchase #2	$89.68	12.338%	$100.7447	$100.74	$100.75	$100.70
Purchase #3	$208.62	7.116%	$223.4654	$223.47	$223.45	$223.50
Purchase #4	$35.73	7.554%	$38.429	$38.43	$38.45	$38.40
Purchase #5	$157.46	5.805%	$166.6006	$166.60	$166.60	$166.60
Purchase #6	$40.71	4.766%	$42.6502	$42.65	$42.65	$42.70
Purchase #7	$42.41	5.710%	$44.8316	$44.83	$44.85	$44.80
7 purchase totals =	$766.22		$816.4251	$816.42	$816.45	$816.40