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	$159.25	3.557%	$164.9145	$164.91	$164.90	$164.90
Purchase #2	$205.96	6.649%	$219.6543	$219.65	$219.65	$219.70
Purchase #3	$38.75	9.828%	$42.5584	$42.56	$42.55	$42.60
Purchase #4	$148.52	8.858%	$161.6759	$161.68	$161.70	$161.70
Purchase #5	$41.66	7.800%	$44.9095	$44.91	$44.90	$44.90
Purchase #6	$6.74	8.509%	$7.3135	$7.31	$7.30	$7.30
Purchase #7	$97.66	3.291%	$100.874	$100.87	$100.85	$100.90
7 purchase totals =	$698.54		$741.9001	$741.89	$741.85	$742.00