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	$124.83	12.464%	$140.3888	$140.39	$140.40	$140.40
Purchase #2	$123.59	7.609%	$132.994	$132.99	$133.00	$133.00
Purchase #3	$196.41	10.463%	$216.9604	$216.96	$216.95	$217.00
Purchase #4	$63.80	13.559%	$72.4506	$72.45	$72.45	$72.50
Purchase #5	$175.46	11.811%	$196.1836	$196.18	$196.20	$196.20
Purchase #6	$221.44	13.515%	$251.3676	$251.37	$251.35	$251.40
Purchase #7	$107.46	5.613%	$113.4917	$113.49	$113.50	$113.50
7 purchase totals =	$1,012.99		$1,123.8367	$1,123.83	$1,123.85	$1,124.00