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	$145.56	10.635%	$161.0403	$161.04	$161.05	$161.00
Purchase #2	$54.81	4.229%	$57.1279	$57.13	$57.15	$57.10
Purchase #3	$250.81	11.819%	$280.4532	$280.45	$280.45	$280.50
Purchase #4	$224.73	11.449%	$250.4593	$250.46	$250.45	$250.50
Purchase #5	$50.96	7.160%	$54.6087	$54.61	$54.60	$54.60
Purchase #6	$8.70	10.487%	$9.6124	$9.61	$9.60	$9.60
Purchase #7	$190.95	7.241%	$204.7767	$204.78	$204.80	$204.80
7 purchase totals =	$926.52		$1,018.0785	$1,018.08	$1,018.10	$1,018.10