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	$112.90	9.173%	$123.2563	$123.26	$123.25	$123.30
Purchase #2	$78.88	4.331%	$82.2963	$82.30	$82.30	$82.30
Purchase #3	$42.86	4.373%	$44.7343	$44.73	$44.75	$44.70
Purchase #4	$247.70	12.288%	$278.1374	$278.14	$278.15	$278.10
Purchase #5	$61.50	7.733%	$66.2558	$66.26	$66.25	$66.30
Purchase #6	$51.86	10.389%	$57.2477	$57.25	$57.25	$57.20
Purchase #7	$174.39	7.355%	$187.2164	$187.22	$187.20	$187.20
7 purchase totals =	$770.09		$839.1442	$839.16	$839.15	$839.10