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	$11.53	5.479%	$12.1617	$12.16	$12.15	$12.20
Purchase #2	$145.94	13.729%	$165.9761	$165.98	$166.00	$166.00
Purchase #3	$166.28	12.460%	$186.9985	$187.00	$187.00	$187.00
Purchase #4	$87.56	12.561%	$98.5584	$98.56	$98.55	$98.60
Purchase #5	$36.56	10.546%	$40.4156	$40.42	$40.40	$40.40
Purchase #6	$138.32	6.325%	$147.0687	$147.07	$147.05	$147.10
Purchase #7	$137.54	13.547%	$156.1725	$156.17	$156.15	$156.20
7 purchase totals =	$723.73		$807.3515	$807.36	$807.30	$807.50