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	$85.25	9.340%	$93.2124	$93.21	$93.20	$93.20
Purchase #2	$69.72	12.213%	$78.2349	$78.23	$78.25	$78.20
Purchase #3	$78.84	13.595%	$89.5583	$89.56	$89.55	$89.60
Purchase #4	$131.63	11.280%	$146.4779	$146.48	$146.50	$146.50
Purchase #5	$228.55	4.129%	$237.9868	$237.99	$238.00	$238.00
Purchase #6	$56.48	4.686%	$59.1267	$59.13	$59.15	$59.10
Purchase #7	$219.58	3.149%	$226.4946	$226.49	$226.50	$226.50
7 purchase totals =	$870.05		$931.0916	$931.09	$931.15	$931.10