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	$68.62	6.255%	$72.9122	$72.91	$72.90	$72.90
Purchase #2	$214.32	5.375%	$225.8397	$225.84	$225.85	$225.80
Purchase #3	$169.94	12.473%	$191.1366	$191.14	$191.15	$191.10
Purchase #4	$31.87	4.262%	$33.2283	$33.23	$33.25	$33.20
Purchase #5	$152.56	10.707%	$168.8946	$168.89	$168.90	$168.90
Purchase #6	$206.94	3.867%	$214.9424	$214.94	$214.95	$214.90
Purchase #7	$116.50	3.190%	$120.2164	$120.22	$120.20	$120.20
7 purchase totals =	$960.75		$1,027.1702	$1,027.17	$1,027.20	$1,027.00