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	$42.41	6.111%	$45.0017	$45.00	$45.00	$45.00
Purchase #2	$144.90	6.693%	$154.5982	$154.60	$154.60	$154.60
Purchase #3	$153.34	12.178%	$172.0137	$172.01	$172.00	$172.00
Purchase #4	$110.75	8.588%	$120.2612	$120.26	$120.25	$120.30
Purchase #5	$43.96	9.865%	$48.2967	$48.30	$48.30	$48.30
Purchase #6	$206.67	9.288%	$225.8655	$225.87	$225.85	$225.90
Purchase #7	$93.96	6.690%	$100.2459	$100.25	$100.25	$100.20
7 purchase totals =	$795.99		$866.2829	$866.29	$866.25	$866.30