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	$31.46	7.758%	$33.9007	$33.90	$33.90	$33.90
Purchase #2	$28.63	9.389%	$31.3181	$31.32	$31.30	$31.30
Purchase #3	$51.52	8.343%	$55.8183	$55.82	$55.80	$55.80
Purchase #4	$38.69	12.256%	$43.4318	$43.43	$43.45	$43.40
Purchase #5	$226.69	7.734%	$244.2222	$244.22	$244.20	$244.20
Purchase #6	$75.82	10.125%	$83.4968	$83.50	$83.50	$83.50
Purchase #7	$125.96	13.198%	$142.5842	$142.58	$142.60	$142.60
7 purchase totals =	$578.77		$634.7721	$634.77	$634.75	$634.70