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	$153.85	9.595%	$168.6119	$168.61	$168.60	$168.60
Purchase #2	$135.34	12.232%	$151.8948	$151.89	$151.90	$151.90
Purchase #3	$159.92	5.631%	$168.9251	$168.93	$168.95	$168.90
Purchase #4	$168.81	12.247%	$189.4842	$189.48	$189.50	$189.50
Purchase #5	$106.67	5.513%	$112.5507	$112.55	$112.55	$112.60
Purchase #6	$33.28	6.800%	$35.543	$35.54	$35.55	$35.50
Purchase #7	$10.51	13.314%	$11.9093	$11.91	$11.90	$11.90
7 purchase totals =	$768.38		$838.9190	$838.91	$838.95	$838.90