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	$64.25	3.785%	$66.6819	$66.68	$66.70	$66.70
Purchase #2	$88.33	9.740%	$96.9333	$96.93	$96.95	$96.90
Purchase #3	$158.55	6.583%	$168.9873	$168.99	$169.00	$169.00
Purchase #4	$228.89	11.583%	$255.4023	$255.40	$255.40	$255.40
Purchase #5	$200.25	5.324%	$210.9113	$210.91	$210.90	$210.90
Purchase #6	$167.78	7.391%	$180.1806	$180.18	$180.20	$180.20
Purchase #7	$48.82	6.835%	$52.1568	$52.16	$52.15	$52.20
7 purchase totals =	$956.87		$1,031.2535	$1,031.25	$1,031.30	$1,031.30