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	$247.42	10.462%	$273.3051	$273.31	$273.30	$273.30
Purchase #2	$61.62	5.338%	$64.9093	$64.91	$64.90	$64.90
Purchase #3	$203.62	10.478%	$224.9553	$224.96	$224.95	$225.00
Purchase #4	$84.85	4.247%	$88.4536	$88.45	$88.45	$88.50
Purchase #5	$39.77	11.784%	$44.4565	$44.46	$44.45	$44.50
Purchase #6	$84.52	7.176%	$90.5852	$90.59	$90.60	$90.60
Purchase #7	$201.65	7.174%	$216.1164	$216.12	$216.10	$216.10
7 purchase totals =	$923.45		$1,002.7814	$1,002.80	$1,002.75	$1,002.90