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	$150.34	9.125%	$164.0585	$164.06	$164.05	$164.10
Purchase #2	$219.90	13.839%	$250.332	$250.33	$250.35	$250.30
Purchase #3	$158.70	11.871%	$177.5393	$177.54	$177.55	$177.50
Purchase #4	$56.72	4.218%	$59.1124	$59.11	$59.10	$59.10
Purchase #5	$31.33	11.505%	$34.9345	$34.93	$34.95	$34.90
Purchase #6	$217.43	13.445%	$246.6635	$246.66	$246.65	$246.70
Purchase #7	$54.29	4.786%	$56.8883	$56.89	$56.90	$56.90
7 purchase totals =	$888.71		$989.5285	$989.52	$989.55	$989.50