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	$137.86	11.822%	$154.1578	$154.16	$154.15	$154.20
Purchase #2	$134.82	11.216%	$149.9414	$149.94	$149.95	$149.90
Purchase #3	$76.39	12.384%	$85.8501	$85.85	$85.85	$85.90
Purchase #4	$38.26	10.595%	$42.3136	$42.31	$42.30	$42.30
Purchase #5	$217.43	13.664%	$247.1396	$247.14	$247.15	$247.10
Purchase #6	$132.48	8.626%	$143.9077	$143.91	$143.90	$143.90
Purchase #7	$7.29	7.750%	$7.855	$7.86	$7.85	$7.90
7 purchase totals =	$744.53		$831.1652	$831.17	$831.15	$831.20