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	$121.83	12.549%	$137.1184	$137.12	$137.10	$137.10
Purchase #2	$100.34	11.157%	$111.5349	$111.53	$111.55	$111.50
Purchase #3	$139.61	13.257%	$158.1181	$158.12	$158.10	$158.10
Purchase #4	$116.37	5.277%	$122.5108	$122.51	$122.50	$122.50
Purchase #5	$190.91	13.302%	$216.3048	$216.30	$216.30	$216.30
Purchase #6	$67.27	8.196%	$72.7834	$72.78	$72.80	$72.80
Purchase #7	$217.82	11.572%	$243.0261	$243.03	$243.05	$243.00
7 purchase totals =	$954.15		$1,061.3965	$1,061.39	$1,061.40	$1,061.30