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	$58.70	9.760%	$64.4291	$64.43	$64.45	$64.40
Purchase #2	$244.40	4.559%	$255.5422	$255.54	$255.55	$255.50
Purchase #3	$213.30	12.799%	$240.6003	$240.60	$240.60	$240.60
Purchase #4	$66.82	8.749%	$72.6661	$72.67	$72.65	$72.70
Purchase #5	$63.31	12.763%	$71.3903	$71.39	$71.40	$71.40
Purchase #6	$153.36	3.460%	$158.6663	$158.67	$158.65	$158.70
Purchase #7	$8.43	4.183%	$8.7826	$8.78	$8.80	$8.80
7 purchase totals =	$808.32		$872.0769	$872.08	$872.10	$872.10