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	$78.65	6.287%	$83.5947	$83.59	$83.60	$83.60
Purchase #2	$40.98	11.762%	$45.8001	$45.80	$45.80	$45.80
Purchase #3	$177.78	5.694%	$187.9028	$187.90	$187.90	$187.90
Purchase #4	$157.58	7.457%	$169.3307	$169.33	$169.35	$169.30
Purchase #5	$32.40	9.147%	$35.3636	$35.36	$35.35	$35.40
Purchase #6	$19.66	5.458%	$20.733	$20.73	$20.75	$20.70
Purchase #7	$164.64	4.652%	$172.2991	$172.30	$172.30	$172.30
7 purchase totals =	$671.69		$715.0240	$715.01	$715.05	$715.00