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	$11.70	6.855%	$12.502	$12.50	$12.50	$12.50
Purchase #2	$30.43	6.841%	$32.5117	$32.51	$32.50	$32.50
Purchase #3	$166.90	13.233%	$188.9859	$188.99	$189.00	$189.00
Purchase #4	$52.28	5.548%	$55.1805	$55.18	$55.20	$55.20
Purchase #5	$162.91	6.740%	$173.8901	$173.89	$173.90	$173.90
Purchase #6	$81.26	12.462%	$91.3866	$91.39	$91.40	$91.40
Purchase #7	$76.61	8.219%	$82.9066	$82.91	$82.90	$82.90
7 purchase totals =	$582.09		$637.3634	$637.37	$637.40	$637.40