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	$62.37	6.330%	$66.318	$66.32	$66.30	$66.30
Purchase #2	$101.80	6.490%	$108.4068	$108.41	$108.40	$108.40
Purchase #3	$127.51	10.564%	$140.9802	$140.98	$141.00	$141.00
Purchase #4	$53.78	9.784%	$59.0418	$59.04	$59.05	$59.00
Purchase #5	$230.35	8.562%	$250.0726	$250.07	$250.05	$250.10
Purchase #6	$65.38	7.640%	$70.375	$70.38	$70.40	$70.40
Purchase #7	$61.35	6.827%	$65.5384	$65.54	$65.55	$65.50
7 purchase totals =	$702.54		$760.7328	$760.74	$760.75	$760.70