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	$30.83	6.554%	$32.8506	$32.85	$32.85	$32.90
Purchase #2	$223.58	11.269%	$248.7752	$248.78	$248.80	$248.80
Purchase #3	$122.41	7.692%	$131.8258	$131.83	$131.85	$131.80
Purchase #4	$228.36	7.615%	$245.7496	$245.75	$245.75	$245.70
Purchase #5	$97.26	12.637%	$109.5507	$109.55	$109.55	$109.60
Purchase #6	$57.73	3.278%	$59.6224	$59.62	$59.60	$59.60
Purchase #7	$40.90	10.635%	$45.2497	$45.25	$45.25	$45.20
7 purchase totals =	$801.07		$873.6240	$873.63	$873.65	$873.60