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	$211.77	6.203%	$224.9061	$224.91	$224.90	$224.90
Purchase #2	$35.82	12.767%	$40.3931	$40.39	$40.40	$40.40
Purchase #3	$143.56	11.791%	$160.4872	$160.49	$160.50	$160.50
Purchase #4	$207.31	12.128%	$232.4526	$232.45	$232.45	$232.50
Purchase #5	$67.96	8.129%	$73.4845	$73.48	$73.50	$73.50
Purchase #6	$139.75	13.478%	$158.5855	$158.59	$158.60	$158.60
Purchase #7	$243.37	12.775%	$274.4605	$274.46	$274.45	$274.50
7 purchase totals =	$1,049.54		$1,164.7695	$1,164.77	$1,164.80	$1,164.90