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	$203.48	10.753%	$225.3602	$225.36	$225.35	$225.40
Purchase #2	$100.38	5.272%	$105.672	$105.67	$105.65	$105.70
Purchase #3	$90.31	6.155%	$95.8686	$95.87	$95.85	$95.90
Purchase #4	$74.73	3.401%	$77.2716	$77.27	$77.25	$77.30
Purchase #5	$116.77	13.486%	$132.5176	$132.52	$132.50	$132.50
Purchase #6	$162.49	6.410%	$172.9056	$172.91	$172.90	$172.90
Purchase #7	$20.65	5.556%	$21.7973	$21.80	$21.80	$21.80
7 purchase totals =	$768.81		$831.3929	$831.40	$831.30	$831.50