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	$18.88	12.305%	$21.2032	$21.20	$21.20	$21.20
Purchase #2	$237.46	3.346%	$245.4054	$245.41	$245.40	$245.40
Purchase #3	$33.59	6.620%	$35.8137	$35.81	$35.80	$35.80
Purchase #4	$244.91	12.476%	$275.465	$275.47	$275.45	$275.50
Purchase #5	$247.84	10.504%	$273.8731	$273.87	$273.85	$273.90
Purchase #6	$132.43	9.285%	$144.7261	$144.73	$144.75	$144.70
Purchase #7	$20.71	5.516%	$21.8524	$21.85	$21.85	$21.90
7 purchase totals =	$935.82		$1,018.3389	$1,018.34	$1,018.30	$1,018.40