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	$82.72	9.635%	$90.6901	$90.69	$90.70	$90.70
Purchase #2	$133.48	8.533%	$144.8698	$144.87	$144.85	$144.90
Purchase #3	$132.65	5.387%	$139.7959	$139.80	$139.80	$139.80
Purchase #4	$173.61	13.220%	$196.5612	$196.56	$196.55	$196.60
Purchase #5	$130.73	7.327%	$140.3086	$140.31	$140.30	$140.30
Purchase #6	$100.88	11.566%	$112.5478	$112.55	$112.55	$112.50
Purchase #7	$54.53	5.529%	$57.545	$57.55	$57.55	$57.50
7 purchase totals =	$808.60		$882.3184	$882.33	$882.30	$882.30