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	$33.43	13.338%	$37.8889	$37.89	$37.90	$37.90
Purchase #2	$53.67	4.182%	$55.9145	$55.91	$55.90	$55.90
Purchase #3	$165.85	10.162%	$182.7037	$182.70	$182.70	$182.70
Purchase #4	$202.77	12.349%	$227.8101	$227.81	$227.80	$227.80
Purchase #5	$69.33	5.193%	$72.9303	$72.93	$72.95	$72.90
Purchase #6	$10.62	11.297%	$11.8197	$11.82	$11.80	$11.80
Purchase #7	$207.96	13.591%	$236.2238	$236.22	$236.20	$236.20
7 purchase totals =	$743.63		$825.2910	$825.28	$825.25	$825.20