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	$13.43	3.249%	$13.8663	$13.87	$13.85	$13.90
Purchase #2	$109.94	8.470%	$119.2519	$119.25	$119.25	$119.30
Purchase #3	$120.34	3.187%	$124.1752	$124.18	$124.20	$124.20
Purchase #4	$173.46	3.665%	$179.8173	$179.82	$179.80	$179.80
Purchase #5	$111.76	7.831%	$120.5119	$120.51	$120.50	$120.50
Purchase #6	$160.85	7.165%	$172.3749	$172.37	$172.35	$172.40
Purchase #7	$247.38	11.559%	$275.9747	$275.97	$275.95	$276.00
7 purchase totals =	$937.16		$1,005.9722	$1,005.97	$1,005.90	$1,006.10