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	$86.78	3.872%	$90.1401	$90.14	$90.15	$90.10
Purchase #2	$243.30	10.489%	$268.8197	$268.82	$268.80	$268.80
Purchase #3	$37.43	4.253%	$39.0219	$39.02	$39.00	$39.00
Purchase #4	$112.53	8.575%	$122.1794	$122.18	$122.20	$122.20
Purchase #5	$78.42	3.149%	$80.8894	$80.89	$80.90	$80.90
Purchase #6	$163.95	4.550%	$171.4097	$171.41	$171.40	$171.40
Purchase #7	$38.64	4.777%	$40.4858	$40.49	$40.50	$40.50
7 purchase totals =	$761.05		$812.9460	$812.95	$812.95	$812.90