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	$117.53	4.854%	$123.2349	$123.23	$123.25	$123.20
Purchase #2	$27.64	11.359%	$30.7796	$30.78	$30.80	$30.80
Purchase #3	$73.57	6.256%	$78.1725	$78.17	$78.15	$78.20
Purchase #4	$123.31	11.802%	$137.863	$137.86	$137.85	$137.90
Purchase #5	$158.60	9.208%	$173.2039	$173.20	$173.20	$173.20
Purchase #6	$108.46	10.431%	$119.7735	$119.77	$119.75	$119.80
Purchase #7	$229.53	9.262%	$250.7891	$250.79	$250.80	$250.80
7 purchase totals =	$838.64		$913.8165	$913.80	$913.80	$913.90