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	$12.73	4.793%	$13.3401	$13.34	$13.35	$13.30
Purchase #2	$187.45	13.641%	$213.0201	$213.02	$213.00	$213.00
Purchase #3	$7.98	12.526%	$8.9796	$8.98	$9.00	$9.00
Purchase #4	$45.55	13.791%	$51.8318	$51.83	$51.85	$51.80
Purchase #5	$237.41	10.567%	$262.4971	$262.50	$262.50	$262.50
Purchase #6	$228.52	12.392%	$256.8382	$256.84	$256.85	$256.80
Purchase #7	$177.89	10.659%	$196.8513	$196.85	$196.85	$196.90
7 purchase totals =	$897.53		$1,003.3582	$1,003.36	$1,003.40	$1,003.30