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	$225.89	10.449%	$249.4932	$249.49	$249.50	$249.50
Purchase #2	$82.74	11.247%	$92.0458	$92.05	$92.05	$92.00
Purchase #3	$87.63	8.232%	$94.8437	$94.84	$94.85	$94.80
Purchase #4	$183.91	3.440%	$190.2365	$190.24	$190.25	$190.20
Purchase #5	$200.45	7.419%	$215.3214	$215.32	$215.30	$215.30
Purchase #6	$153.68	11.589%	$171.49	$171.49	$171.50	$171.50
Purchase #7	$189.62	12.799%	$213.8895	$213.89	$213.90	$213.90
7 purchase totals =	$1,123.92		$1,227.3201	$1,227.32	$1,227.35	$1,227.20