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	$42.84	13.291%	$48.5339	$48.53	$48.55	$48.50
Purchase #2	$49.67	10.514%	$54.8923	$54.89	$54.90	$54.90
Purchase #3	$108.32	12.536%	$121.899	$121.90	$121.90	$121.90
Purchase #4	$72.95	7.562%	$78.4665	$78.47	$78.45	$78.50
Purchase #5	$101.92	3.644%	$105.634	$105.63	$105.65	$105.60
Purchase #6	$18.34	13.322%	$20.7833	$20.78	$20.80	$20.80
Purchase #7	$191.73	4.199%	$199.7807	$199.78	$199.80	$199.80
7 purchase totals =	$585.77		$629.9897	$629.98	$630.05	$630.00