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	$20.54	4.418%	$21.4475	$21.45	$21.45	$21.40
Purchase #2	$35.62	8.194%	$38.5387	$38.54	$38.55	$38.50
Purchase #3	$234.79	4.797%	$246.0529	$246.05	$246.05	$246.10
Purchase #4	$242.43	10.109%	$266.9372	$266.94	$266.95	$266.90
Purchase #5	$100.40	11.508%	$111.954	$111.95	$111.95	$112.00
Purchase #6	$75.60	8.679%	$82.1613	$82.16	$82.15	$82.20
Purchase #7	$184.34	13.864%	$209.8969	$209.90	$209.90	$209.90
7 purchase totals =	$893.72		$976.9885	$976.99	$977.00	$977.00