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	$18.43	11.296%	$20.5119	$20.51	$20.50	$20.50
Purchase #2	$24.89	4.102%	$25.911	$25.91	$25.90	$25.90
Purchase #3	$118.62	11.245%	$131.9588	$131.96	$131.95	$132.00
Purchase #4	$137.72	7.184%	$147.6138	$147.61	$147.60	$147.60
Purchase #5	$83.96	3.595%	$86.9784	$86.98	$87.00	$87.00
Purchase #6	$22.80	13.209%	$25.8117	$25.81	$25.80	$25.80
Purchase #7	$78.95	3.231%	$81.5009	$81.50	$81.50	$81.50
7 purchase totals =	$485.37		$520.2865	$520.28	$520.25	$520.30