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	$38.80	6.289%	$41.2401	$41.24	$41.25	$41.20
Purchase #2	$87.46	5.747%	$92.4863	$92.49	$92.50	$92.50
Purchase #3	$35.57	8.235%	$38.4992	$38.50	$38.50	$38.50
Purchase #4	$238.89	4.161%	$248.8302	$248.83	$248.85	$248.80
Purchase #5	$50.98	11.849%	$57.0206	$57.02	$57.00	$57.00
Purchase #6	$201.82	11.772%	$225.5783	$225.58	$225.60	$225.60
Purchase #7	$69.31	4.499%	$72.4283	$72.43	$72.45	$72.40
7 purchase totals =	$722.83		$776.0830	$776.09	$776.15	$776.00