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	$41.79	6.478%	$44.4972	$44.50	$44.50	$44.50
Purchase #2	$243.96	12.521%	$274.5062	$274.51	$274.50	$274.50
Purchase #3	$60.59	8.719%	$65.8728	$65.87	$65.85	$65.90
Purchase #4	$166.53	3.329%	$172.0738	$172.07	$172.05	$172.10
Purchase #5	$104.28	7.800%	$112.4138	$112.41	$112.40	$112.40
Purchase #6	$88.37	6.865%	$94.4366	$94.44	$94.45	$94.40
Purchase #7	$27.58	6.798%	$29.4549	$29.45	$29.45	$29.50
7 purchase totals =	$733.10		$793.2553	$793.25	$793.20	$793.30