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	$200.83	13.230%	$227.3998	$227.40	$227.40	$227.40
Purchase #2	$6.89	10.232%	$7.595	$7.60	$7.60	$7.60
Purchase #3	$169.31	8.384%	$183.505	$183.51	$183.50	$183.50
Purchase #4	$166.37	8.430%	$180.395	$180.40	$180.40	$180.40
Purchase #5	$191.56	6.496%	$204.0037	$204.00	$204.00	$204.00
Purchase #6	$68.81	5.367%	$72.503	$72.50	$72.50	$72.50
Purchase #7	$32.76	8.385%	$35.5069	$35.51	$35.50	$35.50
7 purchase totals =	$836.53		$910.9084	$910.92	$910.90	$910.90