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	$10.71	6.537%	$11.4101	$11.41	$11.40	$11.40
Purchase #2	$89.42	12.797%	$100.8631	$100.86	$100.85	$100.90
Purchase #3	$143.82	4.873%	$150.8283	$150.83	$150.85	$150.80
Purchase #4	$235.30	6.400%	$250.3592	$250.36	$250.35	$250.40
Purchase #5	$161.89	8.139%	$175.0662	$175.07	$175.05	$175.10
Purchase #6	$184.42	3.475%	$190.8286	$190.83	$190.85	$190.80
Purchase #7	$111.33	6.325%	$118.3716	$118.37	$118.35	$118.40
7 purchase totals =	$936.89		$997.7271	$997.73	$997.70	$997.80