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	$42.65	13.455%	$48.3886	$48.39	$48.40	$48.40
Purchase #2	$124.84	12.448%	$140.3801	$140.38	$140.40	$140.40
Purchase #3	$117.85	5.505%	$124.3376	$124.34	$124.35	$124.30
Purchase #4	$238.46	5.551%	$251.6969	$251.70	$251.70	$251.70
Purchase #5	$206.85	3.706%	$214.5159	$214.52	$214.50	$214.50
Purchase #6	$33.76	11.713%	$37.7143	$37.71	$37.70	$37.70
Purchase #7	$232.63	13.602%	$264.2723	$264.27	$264.25	$264.30
7 purchase totals =	$997.04		$1,081.3057	$1,081.31	$1,081.30	$1,081.30