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	$105.83	6.349%	$112.5491	$112.55	$112.55	$112.50
Purchase #2	$18.29	6.488%	$19.4767	$19.48	$19.50	$19.50
Purchase #3	$238.25	12.460%	$267.936	$267.94	$267.95	$267.90
Purchase #4	$76.42	4.789%	$80.0798	$80.08	$80.10	$80.10
Purchase #5	$127.43	10.534%	$140.8535	$140.85	$140.85	$140.90
Purchase #6	$168.65	11.340%	$187.7749	$187.77	$187.75	$187.80
Purchase #7	$36.96	10.464%	$40.8275	$40.83	$40.85	$40.80
7 purchase totals =	$771.83		$849.4975	$849.50	$849.55	$849.50