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	$44.47	13.627%	$50.5299	$50.53	$50.55	$50.50
Purchase #2	$165.86	6.379%	$176.4402	$176.44	$176.45	$176.40
Purchase #3	$123.29	11.508%	$137.4782	$137.48	$137.50	$137.50
Purchase #4	$131.78	7.308%	$141.4105	$141.41	$141.40	$141.40
Purchase #5	$49.74	9.285%	$54.3584	$54.36	$54.35	$54.40
Purchase #6	$211.80	10.798%	$234.6702	$234.67	$234.65	$234.70
Purchase #7	$169.43	5.410%	$178.5962	$178.60	$178.60	$178.60
7 purchase totals =	$896.37		$973.4836	$973.49	$973.50	$973.50