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	$119.91	3.769%	$124.4294	$124.43	$124.45	$124.40
Purchase #2	$55.94	13.464%	$63.4718	$63.47	$63.45	$63.50
Purchase #3	$35.73	13.357%	$40.5025	$40.50	$40.50	$40.50
Purchase #4	$75.31	8.249%	$81.5223	$81.52	$81.50	$81.50
Purchase #5	$99.65	11.303%	$110.9134	$110.91	$110.90	$110.90
Purchase #6	$204.49	13.259%	$231.6033	$231.60	$231.60	$231.60
Purchase #7	$170.50	8.861%	$185.608	$185.61	$185.60	$185.60
7 purchase totals =	$761.53		$838.0507	$838.04	$838.00	$838.00