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	$89.50	12.668%	$100.8379	$100.84	$100.85	$100.80
Purchase #2	$146.94	10.637%	$162.57	$162.57	$162.55	$162.60
Purchase #3	$79.85	4.347%	$83.3211	$83.32	$83.30	$83.30
Purchase #4	$246.25	10.502%	$272.1112	$272.11	$272.10	$272.10
Purchase #5	$155.94	13.456%	$176.9233	$176.92	$176.90	$176.90
Purchase #6	$145.82	6.468%	$155.2516	$155.25	$155.25	$155.30
Purchase #7	$149.25	8.103%	$161.3437	$161.34	$161.35	$161.30
7 purchase totals =	$1,013.55		$1,112.3588	$1,112.35	$1,112.30	$1,112.30