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	$235.83	8.334%	$255.4841	$255.48	$255.50	$255.50
Purchase #2	$203.89	7.519%	$219.2205	$219.22	$219.20	$219.20
Purchase #3	$67.61	13.851%	$76.9747	$76.97	$76.95	$77.00
Purchase #4	$33.67	12.526%	$37.8875	$37.89	$37.90	$37.90
Purchase #5	$9.96	5.739%	$10.5316	$10.53	$10.55	$10.50
Purchase #6	$91.84	10.218%	$101.2242	$101.22	$101.20	$101.20
Purchase #7	$130.29	12.255%	$146.257	$146.26	$146.25	$146.30
7 purchase totals =	$773.09		$847.5796	$847.57	$847.55	$847.60