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	$231.78	4.624%	$242.4975	$242.50	$242.50	$242.50
Purchase #2	$158.60	13.581%	$180.1395	$180.14	$180.15	$180.10
Purchase #3	$144.71	10.768%	$160.2924	$160.29	$160.30	$160.30
Purchase #4	$203.42	6.404%	$216.447	$216.45	$216.45	$216.40
Purchase #5	$40.85	11.471%	$45.5359	$45.54	$45.55	$45.50
Purchase #6	$92.59	8.231%	$100.2111	$100.21	$100.20	$100.20
Purchase #7	$168.61	10.535%	$186.3731	$186.37	$186.35	$186.40
7 purchase totals =	$1,040.56		$1,131.4965	$1,131.50	$1,131.50	$1,131.40