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	$167.90	13.257%	$190.1585	$190.16	$190.15	$190.20
Purchase #2	$24.56	7.175%	$26.3222	$26.32	$26.30	$26.30
Purchase #3	$34.81	10.165%	$38.3484	$38.35	$38.35	$38.30
Purchase #4	$100.54	8.679%	$109.2659	$109.27	$109.25	$109.30
Purchase #5	$127.69	9.339%	$139.615	$139.62	$139.60	$139.60
Purchase #6	$162.78	4.367%	$169.8886	$169.89	$169.90	$169.90
Purchase #7	$122.65	8.402%	$132.9551	$132.96	$132.95	$133.00
7 purchase totals =	$740.93		$806.5537	$806.57	$806.50	$806.60