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	$46.38	11.130%	$51.5421	$51.54	$51.55	$51.50
Purchase #2	$37.50	13.247%	$42.4676	$42.47	$42.45	$42.50
Purchase #3	$67.81	9.198%	$74.0472	$74.05	$74.05	$74.00
Purchase #4	$30.51	6.729%	$32.563	$32.56	$32.55	$32.60
Purchase #5	$93.27	13.580%	$105.9361	$105.94	$105.95	$105.90
Purchase #6	$105.64	7.787%	$113.8662	$113.87	$113.85	$113.90
Purchase #7	$80.96	6.413%	$86.152	$86.15	$86.15	$86.20
7 purchase totals =	$462.07		$506.5742	$506.58	$506.55	$506.60