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	$152.38	6.162%	$161.7697	$161.77	$161.75	$161.80
Purchase #2	$69.29	13.105%	$78.3705	$78.37	$78.35	$78.40
Purchase #3	$90.80	6.580%	$96.7746	$96.77	$96.75	$96.80
Purchase #4	$173.47	13.195%	$196.3594	$196.36	$196.35	$196.40
Purchase #5	$90.35	10.758%	$100.0699	$100.07	$100.05	$100.10
Purchase #6	$37.99	7.226%	$40.7352	$40.74	$40.75	$40.70
Purchase #7	$17.51	12.454%	$19.6907	$19.69	$19.70	$19.70
7 purchase totals =	$631.79		$693.7700	$693.77	$693.70	$693.90