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	$152.78	11.704%	$170.6614	$170.66	$170.65	$170.70
Purchase #2	$154.34	11.273%	$171.7387	$171.74	$171.75	$171.70
Purchase #3	$222.87	13.683%	$253.3653	$253.37	$253.35	$253.40
Purchase #4	$85.66	4.405%	$89.4333	$89.43	$89.45	$89.40
Purchase #5	$70.80	11.405%	$78.8747	$78.87	$78.85	$78.90
Purchase #6	$53.91	3.265%	$55.6702	$55.67	$55.65	$55.70
Purchase #7	$238.99	8.576%	$259.4858	$259.49	$259.50	$259.50
7 purchase totals =	$979.35		$1,079.2294	$1,079.23	$1,079.20	$1,079.30