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	$92.75	6.766%	$99.0255	$99.03	$99.05	$99.00
Purchase #2	$78.85	10.375%	$87.0307	$87.03	$87.05	$87.00
Purchase #3	$113.78	10.812%	$126.0819	$126.08	$126.10	$126.10
Purchase #4	$31.57	11.713%	$35.2678	$35.27	$35.25	$35.30
Purchase #5	$48.80	3.148%	$50.3362	$50.34	$50.35	$50.30
Purchase #6	$92.89	4.302%	$96.8861	$96.89	$96.90	$96.90
Purchase #7	$40.71	9.188%	$44.4504	$44.45	$44.45	$44.50
7 purchase totals =	$499.35		$539.0786	$539.09	$539.15	$539.10