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	$6.69	9.359%	$7.3161	$7.32	$7.30	$7.30
Purchase #2	$79.58	13.329%	$90.1872	$90.19	$90.20	$90.20
Purchase #3	$137.37	3.520%	$142.2054	$142.21	$142.20	$142.20
Purchase #4	$27.86	13.800%	$31.7047	$31.70	$31.70	$31.70
Purchase #5	$174.61	13.571%	$198.3063	$198.31	$198.30	$198.30
Purchase #6	$154.93	4.509%	$161.9158	$161.92	$161.90	$161.90
Purchase #7	$188.88	5.148%	$198.6035	$198.60	$198.60	$198.60
7 purchase totals =	$769.92		$830.2390	$830.25	$830.20	$830.20