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	$7.36	11.714%	$8.2222	$8.22	$8.20	$8.20
Purchase #2	$247.63	11.290%	$275.5874	$275.59	$275.60	$275.60
Purchase #3	$59.25	11.515%	$66.0726	$66.07	$66.05	$66.10
Purchase #4	$238.89	11.527%	$266.4269	$266.43	$266.45	$266.40
Purchase #5	$242.67	12.262%	$272.4262	$272.43	$272.45	$272.40
Purchase #6	$137.52	12.383%	$154.5491	$154.55	$154.55	$154.50
Purchase #7	$33.56	5.658%	$35.4588	$35.46	$35.45	$35.50
7 purchase totals =	$966.88		$1,078.7432	$1,078.75	$1,078.75	$1,078.70