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	$27.87	13.762%	$31.7055	$31.71	$31.70	$31.70
Purchase #2	$36.31	3.312%	$37.5126	$37.51	$37.50	$37.50
Purchase #3	$47.71	6.213%	$50.6742	$50.67	$50.65	$50.70
Purchase #4	$138.71	11.756%	$155.0167	$155.02	$155.00	$155.00
Purchase #5	$54.78	12.584%	$61.6735	$61.67	$61.65	$61.70
Purchase #6	$101.81	7.872%	$109.8245	$109.82	$109.80	$109.80
Purchase #7	$50.93	8.722%	$55.3721	$55.37	$55.35	$55.40
7 purchase totals =	$458.12		$501.7791	$501.77	$501.65	$501.80