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	$60.36	3.766%	$62.6332	$62.63	$62.65	$62.60
Purchase #2	$88.38	12.231%	$99.1898	$99.19	$99.20	$99.20
Purchase #3	$160.30	8.357%	$173.6963	$173.70	$173.70	$173.70
Purchase #4	$98.72	13.329%	$111.8784	$111.88	$111.90	$111.90
Purchase #5	$70.55	13.828%	$80.3057	$80.31	$80.30	$80.30
Purchase #6	$44.65	12.682%	$50.3125	$50.31	$50.30	$50.30
Purchase #7	$75.77	10.549%	$83.763	$83.76	$83.75	$83.80
7 purchase totals =	$598.73		$661.7789	$661.78	$661.80	$661.80