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	$240.53	6.160%	$255.3466	$255.35	$255.35	$255.30
Purchase #2	$233.25	13.406%	$264.5195	$264.52	$264.50	$264.50
Purchase #3	$161.26	13.817%	$183.5413	$183.54	$183.55	$183.50
Purchase #4	$13.67	12.649%	$15.3991	$15.40	$15.40	$15.40
Purchase #5	$18.50	10.362%	$20.417	$20.42	$20.40	$20.40
Purchase #6	$71.77	8.191%	$77.6487	$77.65	$77.65	$77.60
Purchase #7	$140.98	6.468%	$150.0986	$150.10	$150.10	$150.10
7 purchase totals =	$879.96		$966.9708	$966.98	$966.95	$966.80