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	$18.31	8.275%	$19.8252	$19.83	$19.85	$19.80
Purchase #2	$63.27	10.642%	$70.0032	$70.00	$70.00	$70.00
Purchase #3	$165.42	3.862%	$171.8085	$171.81	$171.80	$171.80
Purchase #4	$149.77	13.149%	$169.4633	$169.46	$169.45	$169.50
Purchase #5	$52.68	7.683%	$56.7274	$56.73	$56.75	$56.70
Purchase #6	$159.56	7.732%	$171.8972	$171.90	$171.90	$171.90
Purchase #7	$208.65	7.294%	$223.8689	$223.87	$223.85	$223.90
7 purchase totals =	$817.66		$883.5937	$883.60	$883.60	$883.60