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	$76.57	11.802%	$85.6068	$85.61	$85.60	$85.60
Purchase #2	$140.40	5.738%	$148.4562	$148.46	$148.45	$148.50
Purchase #3	$227.43	12.134%	$255.0264	$255.03	$255.05	$255.00
Purchase #4	$143.60	8.811%	$156.2526	$156.25	$156.25	$156.30
Purchase #5	$140.42	13.832%	$159.8429	$159.84	$159.85	$159.80
Purchase #6	$57.96	13.135%	$65.573	$65.57	$65.55	$65.60
Purchase #7	$156.30	8.453%	$169.512	$169.51	$169.50	$169.50
7 purchase totals =	$942.68		$1,040.2699	$1,040.27	$1,040.25	$1,040.30