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	$45.63	10.738%	$50.5297	$50.53	$50.55	$50.50
Purchase #2	$132.59	8.215%	$143.4823	$143.48	$143.50	$143.50
Purchase #3	$38.62	7.361%	$41.4628	$41.46	$41.45	$41.50
Purchase #4	$92.85	6.163%	$98.5723	$98.57	$98.55	$98.60
Purchase #5	$246.39	11.502%	$274.7298	$274.73	$274.75	$274.70
Purchase #6	$236.83	7.196%	$253.8723	$253.87	$253.85	$253.90
Purchase #7	$27.75	7.867%	$29.9331	$29.93	$29.95	$29.90
7 purchase totals =	$820.66		$892.5823	$892.57	$892.60	$892.60