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	$40.40	5.301%	$42.5416	$42.54	$42.55	$42.50
Purchase #2	$185.67	10.315%	$204.8219	$204.82	$204.80	$204.80
Purchase #3	$225.36	13.301%	$255.3351	$255.34	$255.35	$255.30
Purchase #4	$110.61	11.596%	$123.4363	$123.44	$123.45	$123.40
Purchase #5	$213.77	9.723%	$234.5549	$234.55	$234.55	$234.60
Purchase #6	$239.41	13.628%	$272.0368	$272.04	$272.05	$272.00
Purchase #7	$77.77	7.189%	$83.3609	$83.36	$83.35	$83.40
7 purchase totals =	$1,092.99		$1,216.0875	$1,216.09	$1,216.10	$1,216.00