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	$46.34	5.256%	$48.7756	$48.78	$48.80	$48.80
Purchase #2	$97.93	9.840%	$107.5663	$107.57	$107.55	$107.60
Purchase #3	$78.89	8.184%	$85.3464	$85.35	$85.35	$85.30
Purchase #4	$55.43	5.552%	$58.5075	$58.51	$58.50	$58.50
Purchase #5	$242.65	13.518%	$275.4514	$275.45	$275.45	$275.50
Purchase #6	$75.58	13.633%	$85.8838	$85.88	$85.90	$85.90
Purchase #7	$22.77	11.293%	$25.3414	$25.34	$25.35	$25.30
7 purchase totals =	$619.59		$686.8724	$686.88	$686.90	$686.90