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	$7.93	6.517%	$8.4468	$8.45	$8.45	$8.40
Purchase #2	$40.78	11.105%	$45.3086	$45.31	$45.30	$45.30
Purchase #3	$196.64	6.724%	$209.8621	$209.86	$209.85	$209.90
Purchase #4	$18.92	13.389%	$21.4532	$21.45	$21.45	$21.50
Purchase #5	$84.40	8.442%	$91.525	$91.53	$91.55	$91.50
Purchase #6	$121.31	7.785%	$130.754	$130.75	$130.75	$130.80
Purchase #7	$44.60	3.754%	$46.2743	$46.27	$46.25	$46.30
7 purchase totals =	$514.58		$553.6240	$553.62	$553.60	$553.70