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	$123.77	6.197%	$131.44	$131.44	$131.45	$131.40
Purchase #2	$33.60	3.679%	$34.8361	$34.84	$34.85	$34.80
Purchase #3	$116.66	6.503%	$124.2464	$124.25	$124.25	$124.20
Purchase #4	$128.92	9.581%	$141.2718	$141.27	$141.25	$141.30
Purchase #5	$86.97	9.498%	$95.2304	$95.23	$95.25	$95.20
Purchase #6	$179.34	8.675%	$194.8977	$194.90	$194.90	$194.90
Purchase #7	$9.61	9.495%	$10.5225	$10.52	$10.50	$10.50
7 purchase totals =	$678.87		$732.4449	$732.45	$732.45	$732.30