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	$66.94	6.472%	$71.2724	$71.27	$71.25	$71.30
Purchase #2	$121.49	10.869%	$134.6947	$134.69	$134.70	$134.70
Purchase #3	$144.76	10.535%	$160.0105	$160.01	$160.00	$160.00
Purchase #4	$158.45	8.845%	$172.4649	$172.46	$172.45	$172.50
Purchase #5	$131.81	9.446%	$144.2608	$144.26	$144.25	$144.30
Purchase #6	$137.48	10.273%	$151.6033	$151.60	$151.60	$151.60
Purchase #7	$73.47	7.552%	$79.0185	$79.02	$79.00	$79.00
7 purchase totals =	$834.40		$913.3251	$913.31	$913.25	$913.40