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	$37.60	8.807%	$40.9114	$40.91	$40.90	$40.90
Purchase #2	$78.53	10.414%	$86.7081	$86.71	$86.70	$86.70
Purchase #3	$141.76	9.203%	$154.8062	$154.81	$154.80	$154.80
Purchase #4	$44.61	6.632%	$47.5685	$47.57	$47.55	$47.60
Purchase #5	$189.62	9.831%	$208.2615	$208.26	$208.25	$208.30
Purchase #6	$30.87	3.430%	$31.9288	$31.93	$31.95	$31.90
Purchase #7	$90.34	9.420%	$98.85	$98.85	$98.85	$98.90
7 purchase totals =	$613.33		$669.0345	$669.04	$669.00	$669.10