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	$75.43	11.663%	$84.2274	$84.23	$84.25	$84.20
Purchase #2	$142.96	11.688%	$159.6692	$159.67	$159.65	$159.70
Purchase #3	$35.75	5.548%	$37.7334	$37.73	$37.75	$37.70
Purchase #4	$131.59	3.779%	$136.5628	$136.56	$136.55	$136.60
Purchase #5	$225.72	9.388%	$246.9106	$246.91	$246.90	$246.90
Purchase #6	$233.77	13.299%	$264.8591	$264.86	$264.85	$264.90
Purchase #7	$19.82	8.376%	$21.4801	$21.48	$21.50	$21.50
7 purchase totals =	$865.04		$951.4426	$951.44	$951.45	$951.50