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	$51.30	12.581%	$57.7541	$57.75	$57.75	$57.80
Purchase #2	$172.55	7.571%	$185.6138	$185.61	$185.60	$185.60
Purchase #3	$137.30	13.495%	$155.8286	$155.83	$155.85	$155.80
Purchase #4	$199.83	11.809%	$223.4279	$223.43	$223.45	$223.40
Purchase #5	$44.80	8.306%	$48.5211	$48.52	$48.50	$48.50
Purchase #6	$229.37	11.237%	$255.1443	$255.14	$255.15	$255.10
Purchase #7	$243.76	8.407%	$264.2529	$264.25	$264.25	$264.30
7 purchase totals =	$1,078.91		$1,190.5427	$1,190.53	$1,190.55	$1,190.50