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	$131.27	10.389%	$144.9076	$144.91	$144.90	$144.90
Purchase #2	$210.78	11.405%	$234.8195	$234.82	$234.80	$234.80
Purchase #3	$142.84	11.378%	$159.0923	$159.09	$159.10	$159.10
Purchase #4	$30.80	11.680%	$34.3974	$34.40	$34.40	$34.40
Purchase #5	$58.76	4.686%	$61.5135	$61.51	$61.50	$61.50
Purchase #6	$94.67	9.410%	$103.5784	$103.58	$103.60	$103.60
Purchase #7	$136.74	11.421%	$152.3571	$152.36	$152.35	$152.40
7 purchase totals =	$805.86		$890.6658	$890.67	$890.65	$890.70