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	$53.68	11.289%	$59.7399	$59.74	$59.75	$59.70
Purchase #2	$104.96	4.494%	$109.6769	$109.68	$109.70	$109.70
Purchase #3	$59.96	6.390%	$63.7914	$63.79	$63.80	$63.80
Purchase #4	$120.98	13.436%	$137.2349	$137.23	$137.25	$137.20
Purchase #5	$52.49	10.293%	$57.8928	$57.89	$57.90	$57.90
Purchase #6	$73.41	3.467%	$75.9551	$75.96	$75.95	$76.00
Purchase #7	$82.88	7.554%	$89.1408	$89.14	$89.15	$89.10
7 purchase totals =	$548.36		$593.4318	$593.43	$593.50	$593.40