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	$36.31	6.161%	$38.5471	$38.55	$38.55	$38.50
Purchase #2	$55.41	6.235%	$58.8648	$58.86	$58.85	$58.90
Purchase #3	$137.74	10.392%	$152.0539	$152.05	$152.05	$152.10
Purchase #4	$29.70	8.391%	$32.1921	$32.19	$32.20	$32.20
Purchase #5	$75.43	10.531%	$83.3735	$83.37	$83.35	$83.40
Purchase #6	$66.76	8.323%	$72.3164	$72.32	$72.30	$72.30
Purchase #7	$230.39	5.173%	$242.3081	$242.31	$242.30	$242.30
7 purchase totals =	$631.74		$679.6559	$679.65	$679.60	$679.70