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	$135.54	6.714%	$144.6402	$144.64	$144.65	$144.60
Purchase #2	$95.81	7.822%	$103.3043	$103.30	$103.30	$103.30
Purchase #3	$144.62	4.708%	$151.4287	$151.43	$151.45	$151.40
Purchase #4	$66.40	4.793%	$69.5826	$69.58	$69.60	$69.60
Purchase #5	$31.51	12.440%	$35.4298	$35.43	$35.45	$35.40
Purchase #6	$67.79	11.486%	$75.5764	$75.58	$75.60	$75.60
Purchase #7	$78.67	8.388%	$85.2688	$85.27	$85.25	$85.30
7 purchase totals =	$620.34		$665.2308	$665.23	$665.30	$665.20