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	$147.56	12.812%	$166.4654	$166.47	$166.45	$166.50
Purchase #2	$10.42	3.732%	$10.8089	$10.81	$10.80	$10.80
Purchase #3	$35.71	13.618%	$40.573	$40.57	$40.55	$40.60
Purchase #4	$100.85	4.311%	$105.1976	$105.20	$105.20	$105.20
Purchase #5	$145.96	3.158%	$150.5694	$150.57	$150.55	$150.60
Purchase #6	$28.83	11.151%	$32.0448	$32.04	$32.05	$32.00
Purchase #7	$195.79	5.387%	$206.3372	$206.34	$206.35	$206.30
7 purchase totals =	$665.12		$711.9963	$712.00	$711.95	$712.00