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	$241.85	6.215%	$256.881	$256.88	$256.90	$256.90
Purchase #2	$37.55	3.585%	$38.8962	$38.90	$38.90	$38.90
Purchase #3	$78.89	13.200%	$89.3035	$89.30	$89.30	$89.30
Purchase #4	$179.29	5.163%	$188.5467	$188.55	$188.55	$188.50
Purchase #5	$72.50	7.723%	$78.0992	$78.10	$78.10	$78.10
Purchase #6	$9.78	4.416%	$10.2119	$10.21	$10.20	$10.20
Purchase #7	$131.52	4.778%	$137.804	$137.80	$137.80	$137.80
7 purchase totals =	$751.38		$799.7425	$799.74	$799.75	$799.70