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	$151.60	13.388%	$171.8962	$171.90	$171.90	$171.90
Purchase #2	$221.38	9.549%	$242.5196	$242.52	$242.50	$242.50
Purchase #3	$10.56	7.124%	$11.3123	$11.31	$11.30	$11.30
Purchase #4	$38.94	9.839%	$42.7713	$42.77	$42.75	$42.80
Purchase #5	$77.39	8.347%	$83.8497	$83.85	$83.85	$83.80
Purchase #6	$65.73	3.551%	$68.0641	$68.06	$68.05	$68.10
Purchase #7	$168.80	7.147%	$180.8641	$180.86	$180.85	$180.90
7 purchase totals =	$734.40		$801.2773	$801.27	$801.20	$801.30