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	$7.32	5.285%	$7.7069	$7.71	$7.70	$7.70
Purchase #2	$86.84	10.195%	$95.6933	$95.69	$95.70	$95.70
Purchase #3	$177.55	12.660%	$200.0278	$200.03	$200.05	$200.00
Purchase #4	$80.57	9.226%	$88.0034	$88.00	$88.00	$88.00
Purchase #5	$71.25	10.410%	$78.6671	$78.67	$78.65	$78.70
Purchase #6	$10.41	11.852%	$11.6438	$11.64	$11.65	$11.60
Purchase #7	$71.46	12.679%	$80.5204	$80.52	$80.50	$80.50
7 purchase totals =	$505.40		$562.2627	$562.26	$562.25	$562.20