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	$77.81	13.671%	$88.4474	$88.45	$88.45	$88.40
Purchase #2	$93.85	13.456%	$106.4785	$106.48	$106.50	$106.50
Purchase #3	$45.30	5.790%	$47.9229	$47.92	$47.90	$47.90
Purchase #4	$219.48	8.791%	$238.7745	$238.77	$238.75	$238.80
Purchase #5	$74.34	10.461%	$82.1167	$82.12	$82.10	$82.10
Purchase #6	$84.96	12.603%	$95.6675	$95.67	$95.65	$95.70
Purchase #7	$250.92	12.206%	$281.5473	$281.55	$281.55	$281.50
7 purchase totals =	$846.66		$940.9548	$940.96	$940.90	$940.90