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	$160.28	4.525%	$167.5327	$167.53	$167.55	$167.50
Purchase #2	$128.97	6.284%	$137.0745	$137.07	$137.05	$137.10
Purchase #3	$208.86	4.452%	$218.1584	$218.16	$218.15	$218.20
Purchase #4	$234.41	13.829%	$266.8266	$266.83	$266.85	$266.80
Purchase #5	$247.32	13.790%	$281.4254	$281.43	$281.45	$281.40
Purchase #6	$122.71	13.313%	$139.0464	$139.05	$139.05	$139.00
Purchase #7	$88.52	13.848%	$100.7782	$100.78	$100.80	$100.80
7 purchase totals =	$1,191.07		$1,310.8422	$1,310.85	$1,310.90	$1,310.80