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	$148.85	6.208%	$158.0906	$158.09	$158.10	$158.10
Purchase #2	$160.78	9.111%	$175.4287	$175.43	$175.45	$175.40
Purchase #3	$233.63	7.224%	$250.5074	$250.51	$250.50	$250.50
Purchase #4	$192.32	7.273%	$206.3074	$206.31	$206.30	$206.30
Purchase #5	$59.27	13.594%	$67.3272	$67.33	$67.35	$67.30
Purchase #6	$215.43	13.654%	$244.8448	$244.84	$244.85	$244.80
Purchase #7	$130.80	6.391%	$139.1594	$139.16	$139.15	$139.20
7 purchase totals =	$1,141.08		$1,241.6655	$1,241.67	$1,241.70	$1,241.60