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	$121.37	13.344%	$137.5656	$137.57	$137.55	$137.60
Purchase #2	$71.51	7.534%	$76.8976	$76.90	$76.90	$76.90
Purchase #3	$201.96	12.257%	$226.7142	$226.71	$226.70	$226.70
Purchase #4	$141.42	12.694%	$159.3719	$159.37	$159.35	$159.40
Purchase #5	$80.92	10.378%	$89.3179	$89.32	$89.30	$89.30
Purchase #6	$43.39	10.298%	$47.8583	$47.86	$47.85	$47.90
Purchase #7	$226.54	6.306%	$240.8256	$240.83	$240.85	$240.80
7 purchase totals =	$887.11		$978.5511	$978.56	$978.50	$978.60