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	$132.46	3.380%	$136.9371	$136.94	$136.95	$136.90
Purchase #2	$247.33	11.281%	$275.2313	$275.23	$275.25	$275.20
Purchase #3	$50.61	13.656%	$57.5213	$57.52	$57.50	$57.50
Purchase #4	$30.82	13.354%	$34.9357	$34.94	$34.95	$34.90
Purchase #5	$125.50	4.300%	$130.8965	$130.90	$130.90	$130.90
Purchase #6	$227.97	5.692%	$240.9461	$240.95	$240.95	$240.90
Purchase #7	$103.59	7.284%	$111.1355	$111.14	$111.15	$111.10
7 purchase totals =	$918.28		$987.6035	$987.62	$987.65	$987.40