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	$87.59	13.674%	$99.5671	$99.57	$99.55	$99.60
Purchase #2	$22.90	11.541%	$25.5429	$25.54	$25.55	$25.50
Purchase #3	$136.42	5.672%	$144.1577	$144.16	$144.15	$144.20
Purchase #4	$225.41	6.625%	$240.3434	$240.34	$240.35	$240.30
Purchase #5	$221.45	10.139%	$243.9028	$243.90	$243.90	$243.90
Purchase #6	$5.46	6.690%	$5.8253	$5.83	$5.85	$5.80
Purchase #7	$184.91	13.411%	$209.7083	$209.71	$209.70	$209.70
7 purchase totals =	$884.14		$969.0475	$969.05	$969.05	$969.00