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	$37.74	13.223%	$42.7304	$42.73	$42.75	$42.70
Purchase #2	$187.44	8.511%	$203.393	$203.39	$203.40	$203.40
Purchase #3	$27.76	13.523%	$31.514	$31.51	$31.50	$31.50
Purchase #4	$140.29	10.378%	$154.8493	$154.85	$154.85	$154.80
Purchase #5	$245.49	13.456%	$278.5231	$278.52	$278.50	$278.50
Purchase #6	$84.95	5.264%	$89.4218	$89.42	$89.40	$89.40
Purchase #7	$119.47	10.340%	$131.8232	$131.82	$131.80	$131.80
7 purchase totals =	$843.14		$932.2548	$932.24	$932.20	$932.10