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	$23.46	12.297%	$26.3449	$26.34	$26.35	$26.30
Purchase #2	$233.95	9.819%	$256.9216	$256.92	$256.90	$256.90
Purchase #3	$142.70	11.300%	$158.8251	$158.83	$158.85	$158.80
Purchase #4	$130.74	8.153%	$141.3992	$141.40	$141.40	$141.40
Purchase #5	$66.76	8.629%	$72.5207	$72.52	$72.50	$72.50
Purchase #6	$145.62	8.822%	$158.4666	$158.47	$158.45	$158.50
Purchase #7	$78.42	9.226%	$85.655	$85.66	$85.65	$85.70
7 purchase totals =	$821.65		$900.1331	$900.14	$900.10	$900.10