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	$221.40	12.837%	$249.8211	$249.82	$249.80	$249.80
Purchase #2	$236.78	12.355%	$266.0342	$266.03	$266.05	$266.00
Purchase #3	$205.45	13.152%	$232.4708	$232.47	$232.45	$232.50
Purchase #4	$196.33	12.856%	$221.5702	$221.57	$221.55	$221.60
Purchase #5	$49.50	12.763%	$55.8177	$55.82	$55.80	$55.80
Purchase #6	$150.99	7.383%	$162.1376	$162.14	$162.15	$162.10
Purchase #7	$97.51	8.172%	$105.4785	$105.48	$105.50	$105.50
7 purchase totals =	$1,157.96		$1,293.3301	$1,293.33	$1,293.30	$1,293.30