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	$80.58	6.640%	$85.9305	$85.93	$85.95	$85.90
Purchase #2	$122.92	4.329%	$128.2412	$128.24	$128.25	$128.20
Purchase #3	$38.41	4.258%	$40.0455	$40.05	$40.05	$40.00
Purchase #4	$16.97	9.413%	$18.5674	$18.57	$18.55	$18.60
Purchase #5	$18.71	7.489%	$20.1112	$20.11	$20.10	$20.10
Purchase #6	$138.33	12.147%	$155.1329	$155.13	$155.15	$155.10
Purchase #7	$128.87	11.632%	$143.8602	$143.86	$143.85	$143.90
7 purchase totals =	$544.79		$591.8889	$591.89	$591.90	$591.80