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	$153.96	4.497%	$160.8836	$160.88	$160.90	$160.90
Purchase #2	$132.71	6.604%	$141.4742	$141.47	$141.45	$141.50
Purchase #3	$25.87	11.736%	$28.9061	$28.91	$28.90	$28.90
Purchase #4	$91.74	3.625%	$95.0656	$95.07	$95.05	$95.10
Purchase #5	$33.76	4.420%	$35.2522	$35.25	$35.25	$35.30
Purchase #6	$30.78	11.161%	$34.2154	$34.22	$34.20	$34.20
Purchase #7	$105.88	6.802%	$113.082	$113.08	$113.10	$113.10
7 purchase totals =	$574.70		$608.8791	$608.88	$608.85	$609.00