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	$182.48	9.836%	$200.4287	$200.43	$200.45	$200.40
Purchase #2	$99.78	12.324%	$112.0769	$112.08	$112.10	$112.10
Purchase #3	$158.38	6.361%	$168.4546	$168.45	$168.45	$168.50
Purchase #4	$64.40	6.316%	$68.4675	$68.47	$68.45	$68.50
Purchase #5	$249.58	4.723%	$261.3677	$261.37	$261.35	$261.40
Purchase #6	$36.43	13.863%	$41.4803	$41.48	$41.50	$41.50
Purchase #7	$124.93	13.256%	$141.4907	$141.49	$141.50	$141.50
7 purchase totals =	$915.98		$993.7664	$993.77	$993.80	$993.90