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	$143.30	5.142%	$150.6685	$150.67	$150.65	$150.70
Purchase #2	$33.28	7.807%	$35.8782	$35.88	$35.90	$35.90
Purchase #3	$139.86	8.390%	$151.5943	$151.59	$151.60	$151.60
Purchase #4	$109.56	11.568%	$122.2339	$122.23	$122.25	$122.20
Purchase #5	$139.96	9.222%	$152.8671	$152.87	$152.85	$152.90
Purchase #6	$241.30	9.523%	$264.279	$264.28	$264.30	$264.30
Purchase #7	$32.86	4.505%	$34.3403	$34.34	$34.35	$34.30
7 purchase totals =	$840.12		$911.8613	$911.86	$911.90	$911.90