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	$82.61	3.333%	$85.3634	$85.36	$85.35	$85.40
Purchase #2	$169.51	9.855%	$186.2152	$186.22	$186.20	$186.20
Purchase #3	$92.31	8.723%	$100.3622	$100.36	$100.35	$100.40
Purchase #4	$84.40	12.683%	$95.1045	$95.10	$95.10	$95.10
Purchase #5	$120.88	9.102%	$131.8825	$131.88	$131.90	$131.90
Purchase #6	$43.45	6.829%	$46.4172	$46.42	$46.40	$46.40
Purchase #7	$195.94	4.868%	$205.4784	$205.48	$205.50	$205.50
7 purchase totals =	$789.10		$850.8234	$850.82	$850.80	$850.90