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	$37.47	12.830%	$42.2774	$42.28	$42.30	$42.30
Purchase #2	$38.35	8.114%	$41.4617	$41.46	$41.45	$41.50
Purchase #3	$11.58	7.183%	$12.4118	$12.41	$12.40	$12.40
Purchase #4	$181.45	12.189%	$203.5669	$203.57	$203.55	$203.60
Purchase #5	$249.81	4.282%	$260.5069	$260.51	$260.50	$260.50
Purchase #6	$211.46	4.771%	$221.5488	$221.55	$221.55	$221.50
Purchase #7	$46.71	12.816%	$52.6964	$52.70	$52.70	$52.70
7 purchase totals =	$776.83		$834.4699	$834.48	$834.45	$834.50