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	$12.88	4.680%	$13.4828	$13.48	$13.50	$13.50
Purchase #2	$96.35	7.584%	$103.6572	$103.66	$103.65	$103.70
Purchase #3	$89.33	10.457%	$98.6712	$98.67	$98.65	$98.70
Purchase #4	$247.83	6.715%	$264.4718	$264.47	$264.45	$264.50
Purchase #5	$125.42	10.426%	$138.4963	$138.50	$138.50	$138.50
Purchase #6	$62.96	13.843%	$71.6756	$71.68	$71.70	$71.70
Purchase #7	$128.45	9.625%	$140.8133	$140.81	$140.80	$140.80
7 purchase totals =	$763.22		$831.2682	$831.27	$831.25	$831.40