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	$105.60	13.742%	$120.1116	$120.11	$120.10	$120.10
Purchase #2	$96.50	3.785%	$100.1525	$100.15	$100.15	$100.20
Purchase #3	$228.45	11.775%	$255.35	$255.35	$255.35	$255.40
Purchase #4	$121.74	7.863%	$131.3124	$131.31	$131.30	$131.30
Purchase #5	$80.74	4.213%	$84.1416	$84.14	$84.15	$84.10
Purchase #6	$145.54	5.654%	$153.7688	$153.77	$153.75	$153.80
Purchase #7	$97.55	12.366%	$109.613	$109.61	$109.60	$109.60
7 purchase totals =	$876.12		$954.4499	$954.44	$954.40	$954.50