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	$39.41	7.223%	$42.2566	$42.26	$42.25	$42.30
Purchase #2	$47.87	5.308%	$50.4109	$50.41	$50.40	$50.40
Purchase #3	$174.46	12.574%	$196.3966	$196.40	$196.40	$196.40
Purchase #4	$29.43	8.161%	$31.8318	$31.83	$31.85	$31.80
Purchase #5	$243.30	9.718%	$266.9439	$266.94	$266.95	$266.90
Purchase #6	$130.66	11.652%	$145.8845	$145.88	$145.90	$145.90
Purchase #7	$60.72	10.704%	$67.2195	$67.22	$67.20	$67.20
7 purchase totals =	$725.85		$800.9438	$800.94	$800.95	$800.90