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	$166.58	4.303%	$173.7479	$173.75	$173.75	$173.70
Purchase #2	$76.45	12.199%	$85.7761	$85.78	$85.80	$85.80
Purchase #3	$87.35	8.642%	$94.8988	$94.90	$94.90	$94.90
Purchase #4	$40.50	4.224%	$42.2107	$42.21	$42.20	$42.20
Purchase #5	$103.31	6.184%	$109.6987	$109.70	$109.70	$109.70
Purchase #6	$35.49	11.145%	$39.4454	$39.45	$39.45	$39.40
Purchase #7	$9.59	11.633%	$10.7056	$10.71	$10.70	$10.70
7 purchase totals =	$519.27		$556.4832	$556.50	$556.50	$556.40