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	$38.36	11.612%	$42.8144	$42.81	$42.80	$42.80
Purchase #2	$21.68	13.344%	$24.573	$24.57	$24.55	$24.60
Purchase #3	$146.71	8.179%	$158.7094	$158.71	$158.70	$158.70
Purchase #4	$146.56	5.770%	$155.0165	$155.02	$155.00	$155.00
Purchase #5	$246.27	11.106%	$273.6207	$273.62	$273.60	$273.60
Purchase #6	$201.35	11.205%	$223.9113	$223.91	$223.90	$223.90
Purchase #7	$215.65	12.343%	$242.2677	$242.27	$242.25	$242.30
7 purchase totals =	$1,016.58		$1,120.9130	$1,120.91	$1,120.80	$1,120.90