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	$110.53	9.311%	$120.8214	$120.82	$120.80	$120.80
Purchase #2	$82.94	3.221%	$85.6115	$85.61	$85.60	$85.60
Purchase #3	$84.71	6.769%	$90.444	$90.44	$90.45	$90.40
Purchase #4	$133.51	4.117%	$139.0066	$139.01	$139.00	$139.00
Purchase #5	$110.56	13.315%	$125.2811	$125.28	$125.30	$125.30
Purchase #6	$137.45	8.374%	$148.9601	$148.96	$148.95	$149.00
Purchase #7	$43.60	10.487%	$48.1723	$48.17	$48.15	$48.20
7 purchase totals =	$703.30		$758.2970	$758.29	$758.25	$758.30