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	$235.48	11.214%	$261.8867	$261.89	$261.90	$261.90
Purchase #2	$68.39	12.653%	$77.0434	$77.04	$77.05	$77.00
Purchase #3	$211.60	11.597%	$236.1393	$236.14	$236.15	$236.10
Purchase #4	$95.33	9.274%	$104.1709	$104.17	$104.15	$104.20
Purchase #5	$22.47	8.704%	$24.4258	$24.43	$24.45	$24.40
Purchase #6	$104.34	4.824%	$109.3734	$109.37	$109.35	$109.40
Purchase #7	$40.32	5.376%	$42.4876	$42.49	$42.50	$42.50
7 purchase totals =	$777.93		$855.5271	$855.53	$855.55	$855.50