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	$28.38	11.675%	$31.6934	$31.69	$31.70	$31.70
Purchase #2	$151.94	13.588%	$172.5856	$172.59	$172.60	$172.60
Purchase #3	$165.34	7.189%	$177.2263	$177.23	$177.25	$177.20
Purchase #4	$189.54	6.700%	$202.2392	$202.24	$202.25	$202.20
Purchase #5	$16.61	11.382%	$18.5006	$18.50	$18.50	$18.50
Purchase #6	$190.68	4.689%	$199.621	$199.62	$199.60	$199.60
Purchase #7	$198.86	9.572%	$217.8949	$217.89	$217.90	$217.90
7 purchase totals =	$941.35		$1,019.7610	$1,019.76	$1,019.80	$1,019.70