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	$31.51	9.748%	$34.5816	$34.58	$34.60	$34.60
Purchase #2	$243.88	10.303%	$269.007	$269.01	$269.00	$269.00
Purchase #3	$109.51	12.698%	$123.4156	$123.42	$123.40	$123.40
Purchase #4	$132.87	11.303%	$147.8883	$147.89	$147.90	$147.90
Purchase #5	$243.51	11.653%	$271.8862	$271.89	$271.90	$271.90
Purchase #6	$86.74	3.171%	$89.4905	$89.49	$89.50	$89.50
Purchase #7	$17.93	5.129%	$18.8496	$18.85	$18.85	$18.80
7 purchase totals =	$865.95		$955.1188	$955.13	$955.15	$955.10