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	$39.87	7.636%	$42.9145	$42.91	$42.90	$42.90
Purchase #2	$127.68	4.796%	$133.8035	$133.80	$133.80	$133.80
Purchase #3	$31.40	13.395%	$35.606	$35.61	$35.60	$35.60
Purchase #4	$202.95	4.709%	$212.5069	$212.51	$212.50	$212.50
Purchase #5	$169.70	12.124%	$190.2744	$190.27	$190.25	$190.30
Purchase #6	$109.43	7.254%	$117.3681	$117.37	$117.35	$117.40
Purchase #7	$135.26	11.297%	$150.5403	$150.54	$150.55	$150.50
7 purchase totals =	$816.29		$883.0137	$883.01	$882.95	$883.00