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	$38.52	7.770%	$41.513	$41.51	$41.50	$41.50
Purchase #2	$94.99	12.439%	$106.8058	$106.81	$106.80	$106.80
Purchase #3	$35.89	5.563%	$37.8866	$37.89	$37.90	$37.90
Purchase #4	$85.50	4.404%	$89.2654	$89.27	$89.25	$89.30
Purchase #5	$139.91	11.376%	$155.8262	$155.83	$155.85	$155.80
Purchase #6	$16.38	6.768%	$17.4886	$17.49	$17.50	$17.50
Purchase #7	$205.79	10.353%	$227.0954	$227.10	$227.10	$227.10
7 purchase totals =	$616.98		$675.8810	$675.90	$675.90	$675.90