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	$87.79	12.398%	$98.6742	$98.67	$98.65	$98.70
Purchase #2	$54.48	13.172%	$61.6561	$61.66	$61.65	$61.70
Purchase #3	$218.92	5.105%	$230.0959	$230.10	$230.10	$230.10
Purchase #4	$53.89	10.741%	$59.6783	$59.68	$59.70	$59.70
Purchase #5	$26.91	9.140%	$29.3696	$29.37	$29.35	$29.40
Purchase #6	$208.33	8.284%	$225.5881	$225.59	$225.60	$225.60
Purchase #7	$64.27	5.432%	$67.7611	$67.76	$67.75	$67.80
7 purchase totals =	$714.59		$772.8233	$772.83	$772.80	$773.00