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	$120.95	13.224%	$136.9444	$136.94	$136.95	$136.90
Purchase #2	$51.87	5.181%	$54.5574	$54.56	$54.55	$54.60
Purchase #3	$102.44	6.146%	$108.736	$108.74	$108.75	$108.70
Purchase #4	$39.44	6.233%	$41.8983	$41.90	$41.90	$41.90
Purchase #5	$8.44	12.628%	$9.5058	$9.51	$9.50	$9.50
Purchase #6	$55.77	6.719%	$59.5172	$59.52	$59.50	$59.50
Purchase #7	$169.54	9.671%	$185.9362	$185.94	$185.95	$185.90
7 purchase totals =	$548.45		$597.0953	$597.11	$597.10	$597.00