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	$22.46	7.614%	$24.1701	$24.17	$24.15	$24.20
Purchase #2	$250.89	3.589%	$259.8944	$259.89	$259.90	$259.90
Purchase #3	$127.38	10.691%	$140.9982	$141.00	$141.00	$141.00
Purchase #4	$104.43	4.509%	$109.1387	$109.14	$109.15	$109.10
Purchase #5	$191.95	4.470%	$200.5302	$200.53	$200.55	$200.50
Purchase #6	$183.75	7.523%	$197.5735	$197.57	$197.55	$197.60
Purchase #7	$16.96	9.193%	$18.5191	$18.52	$18.50	$18.50
7 purchase totals =	$897.82		$950.8242	$950.82	$950.80	$950.80