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	$236.30	12.103%	$264.8994	$264.90	$264.90	$264.90
Purchase #2	$74.70	10.617%	$82.6309	$82.63	$82.65	$82.60
Purchase #3	$133.41	7.403%	$143.2863	$143.29	$143.30	$143.30
Purchase #4	$201.81	9.738%	$221.4623	$221.46	$221.45	$221.50
Purchase #5	$101.93	7.214%	$109.2832	$109.28	$109.30	$109.30
Purchase #6	$29.30	13.668%	$33.3047	$33.30	$33.30	$33.30
Purchase #7	$79.79	13.282%	$90.3877	$90.39	$90.40	$90.40
7 purchase totals =	$857.24		$945.2545	$945.25	$945.30	$945.30