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	$11.49	8.421%	$12.4576	$12.46	$12.45	$12.50
Purchase #2	$199.91	10.354%	$220.6087	$220.61	$220.60	$220.60
Purchase #3	$185.91	7.330%	$199.5372	$199.54	$199.55	$199.50
Purchase #4	$94.68	4.340%	$98.7891	$98.79	$98.80	$98.80
Purchase #5	$54.74	5.781%	$57.9045	$57.90	$57.90	$57.90
Purchase #6	$25.37	7.606%	$27.2996	$27.30	$27.30	$27.30
Purchase #7	$129.76	10.870%	$143.8649	$143.86	$143.85	$143.90
7 purchase totals =	$701.86		$760.4616	$760.46	$760.45	$760.50