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	$52.90	11.558%	$59.0142	$59.01	$59.00	$59.00
Purchase #2	$101.71	6.452%	$108.2723	$108.27	$108.25	$108.30
Purchase #3	$23.83	8.348%	$25.8193	$25.82	$25.80	$25.80
Purchase #4	$117.33	12.360%	$131.832	$131.83	$131.85	$131.80
Purchase #5	$116.72	5.525%	$123.1688	$123.17	$123.15	$123.20
Purchase #6	$177.41	7.125%	$190.0505	$190.05	$190.05	$190.10
Purchase #7	$233.29	12.407%	$262.2343	$262.23	$262.25	$262.20
7 purchase totals =	$823.19		$900.3914	$900.38	$900.35	$900.40