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	$93.91	10.128%	$103.4212	$103.42	$103.40	$103.40
Purchase #2	$163.61	11.449%	$182.3417	$182.34	$182.35	$182.30
Purchase #3	$167.27	9.796%	$183.6558	$183.66	$183.65	$183.70
Purchase #4	$20.87	8.417%	$22.6266	$22.63	$22.65	$22.60
Purchase #5	$63.83	4.798%	$66.8926	$66.89	$66.90	$66.90
Purchase #6	$177.92	10.273%	$196.1977	$196.20	$196.20	$196.20
Purchase #7	$86.99	3.342%	$89.8972	$89.90	$89.90	$89.90
7 purchase totals =	$774.40		$845.0328	$845.04	$845.05	$845.00