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	$240.39	6.639%	$256.3495	$256.35	$256.35	$256.30
Purchase #2	$182.51	9.126%	$199.1659	$199.17	$199.15	$199.20
Purchase #3	$92.56	13.310%	$104.8797	$104.88	$104.90	$104.90
Purchase #4	$37.60	8.716%	$40.8772	$40.88	$40.90	$40.90
Purchase #5	$89.64	3.707%	$92.963	$92.96	$92.95	$93.00
Purchase #6	$231.38	9.666%	$253.7452	$253.75	$253.75	$253.70
Purchase #7	$140.66	3.682%	$145.8391	$145.84	$145.85	$145.80
7 purchase totals =	$1,014.74		$1,093.8196	$1,093.83	$1,093.85	$1,093.80