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	$83.42	7.262%	$89.478	$89.48	$89.50	$89.50
Purchase #2	$36.55	7.498%	$39.2905	$39.29	$39.30	$39.30
Purchase #3	$36.96	12.823%	$41.6994	$41.70	$41.70	$41.70
Purchase #4	$189.74	4.575%	$198.4206	$198.42	$198.40	$198.40
Purchase #5	$245.80	13.735%	$279.5606	$279.56	$279.55	$279.60
Purchase #6	$116.48	10.309%	$128.4879	$128.49	$128.50	$128.50
Purchase #7	$80.88	7.594%	$87.022	$87.02	$87.00	$87.00
7 purchase totals =	$789.83		$863.9590	$863.96	$863.95	$864.00