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	$50.54	6.378%	$53.7634	$53.76	$53.75	$53.80
Purchase #2	$40.50	12.278%	$45.4726	$45.47	$45.45	$45.50
Purchase #3	$28.93	10.735%	$32.0356	$32.04	$32.05	$32.00
Purchase #4	$107.94	8.531%	$117.1484	$117.15	$117.15	$117.10
Purchase #5	$123.67	4.624%	$129.3885	$129.39	$129.40	$129.40
Purchase #6	$245.72	4.184%	$256.0009	$256.00	$256.00	$256.00
Purchase #7	$48.80	8.743%	$53.0666	$53.07	$53.05	$53.10
7 purchase totals =	$646.10		$686.8760	$686.88	$686.85	$686.90