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	$97.67	12.246%	$109.6307	$109.63	$109.65	$109.60
Purchase #2	$33.69	4.857%	$35.3263	$35.33	$35.35	$35.30
Purchase #3	$89.86	10.704%	$99.4786	$99.48	$99.50	$99.50
Purchase #4	$238.44	9.729%	$261.6378	$261.64	$261.65	$261.60
Purchase #5	$40.41	10.410%	$44.6167	$44.62	$44.60	$44.60
Purchase #6	$5.46	5.756%	$5.7743	$5.77	$5.75	$5.80
Purchase #7	$58.69	8.800%	$63.8547	$63.85	$63.85	$63.90
7 purchase totals =	$564.22		$620.3191	$620.32	$620.35	$620.30