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	$94.25	9.799%	$103.4856	$103.49	$103.50	$103.50
Purchase #2	$29.72	7.288%	$31.886	$31.89	$31.90	$31.90
Purchase #3	$121.90	3.484%	$126.147	$126.15	$126.15	$126.10
Purchase #4	$32.50	10.520%	$35.919	$35.92	$35.90	$35.90
Purchase #5	$220.62	3.173%	$227.6203	$227.62	$227.60	$227.60
Purchase #6	$19.35	11.499%	$21.5751	$21.58	$21.60	$21.60
Purchase #7	$250.58	13.183%	$283.614	$283.61	$283.60	$283.60
7 purchase totals =	$768.92		$830.2470	$830.26	$830.25	$830.20