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	$100.61	11.686%	$112.3673	$112.37	$112.35	$112.40
Purchase #2	$79.82	13.189%	$90.3475	$90.35	$90.35	$90.30
Purchase #3	$240.83	10.711%	$266.6253	$266.63	$266.65	$266.60
Purchase #4	$31.98	3.754%	$33.1805	$33.18	$33.20	$33.20
Purchase #5	$88.86	12.184%	$99.6867	$99.69	$99.70	$99.70
Purchase #6	$58.49	6.541%	$62.3158	$62.32	$62.30	$62.30
Purchase #7	$154.43	6.406%	$164.3228	$164.32	$164.30	$164.30
7 purchase totals =	$755.02		$828.8459	$828.86	$828.85	$828.80