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	$29.65	10.561%	$32.7813	$32.78	$32.80	$32.80
Purchase #2	$99.86	11.749%	$111.5926	$111.59	$111.60	$111.60
Purchase #3	$246.41	3.820%	$255.8229	$255.82	$255.80	$255.80
Purchase #4	$119.51	3.532%	$123.7311	$123.73	$123.75	$123.70
Purchase #5	$244.95	13.362%	$277.6802	$277.68	$277.70	$277.70
Purchase #6	$244.69	12.104%	$274.3073	$274.31	$274.30	$274.30
Purchase #7	$160.59	5.446%	$169.3357	$169.34	$169.35	$169.30
7 purchase totals =	$1,145.66		$1,245.2511	$1,245.25	$1,245.30	$1,245.20