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	$34.49	3.558%	$35.7172	$35.72	$35.70	$35.70
Purchase #2	$31.51	12.227%	$35.3627	$35.36	$35.35	$35.40
Purchase #3	$169.80	9.287%	$185.5693	$185.57	$185.55	$185.60
Purchase #4	$155.42	7.463%	$167.019	$167.02	$167.00	$167.00
Purchase #5	$24.94	10.544%	$27.5697	$27.57	$27.55	$27.60
Purchase #6	$238.78	7.580%	$256.8795	$256.88	$256.90	$256.90
Purchase #7	$81.52	12.733%	$91.8999	$91.90	$91.90	$91.90
7 purchase totals =	$736.46		$800.0173	$800.02	$799.95	$800.10