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	$26.63	6.522%	$28.3668	$28.37	$28.35	$28.40
Purchase #2	$165.50	8.294%	$179.2266	$179.23	$179.25	$179.20
Purchase #3	$109.70	6.136%	$116.4312	$116.43	$116.45	$116.40
Purchase #4	$135.43	13.130%	$153.212	$153.21	$153.20	$153.20
Purchase #5	$81.98	8.702%	$89.1139	$89.11	$89.10	$89.10
Purchase #6	$40.67	4.374%	$42.4489	$42.45	$42.45	$42.40
Purchase #7	$243.93	10.779%	$270.2232	$270.22	$270.20	$270.20
7 purchase totals =	$803.84		$879.0226	$879.02	$879.00	$878.90