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	$83.53	3.388%	$86.36	$86.36	$86.35	$86.40
Purchase #2	$85.55	4.790%	$89.6478	$89.65	$89.65	$89.60
Purchase #3	$183.70	7.832%	$198.0874	$198.09	$198.10	$198.10
Purchase #4	$65.73	9.758%	$72.1439	$72.14	$72.15	$72.10
Purchase #5	$13.76	10.535%	$15.2096	$15.21	$15.20	$15.20
Purchase #6	$215.63	10.580%	$238.4437	$238.44	$238.45	$238.40
Purchase #7	$203.77	5.785%	$215.5581	$215.56	$215.55	$215.60
7 purchase totals =	$851.67		$915.4505	$915.45	$915.45	$915.40