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	$47.41	4.514%	$49.5501	$49.55	$49.55	$49.60
Purchase #2	$52.48	11.868%	$58.7083	$58.71	$58.70	$58.70
Purchase #3	$243.25	10.396%	$268.5383	$268.54	$268.55	$268.50
Purchase #4	$129.46	3.714%	$134.2681	$134.27	$134.25	$134.30
Purchase #5	$51.66	4.578%	$54.025	$54.03	$54.05	$54.00
Purchase #6	$87.71	3.643%	$90.9053	$90.91	$90.90	$90.90
Purchase #7	$123.49	13.759%	$140.481	$140.48	$140.50	$140.50
7 purchase totals =	$735.46		$796.4761	$796.49	$796.50	$796.50