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	$204.48	7.872%	$220.5767	$220.58	$220.60	$220.60
Purchase #2	$98.82	6.832%	$105.5714	$105.57	$105.55	$105.60
Purchase #3	$239.81	10.228%	$264.3378	$264.34	$264.35	$264.30
Purchase #4	$14.86	6.540%	$15.8318	$15.83	$15.85	$15.80
Purchase #5	$73.50	12.597%	$82.7588	$82.76	$82.75	$82.80
Purchase #6	$45.38	13.610%	$51.5562	$51.56	$51.55	$51.60
Purchase #7	$26.50	4.750%	$27.7588	$27.76	$27.75	$27.80
7 purchase totals =	$703.35		$768.3915	$768.40	$768.40	$768.50