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	$148.80	12.231%	$166.9997	$167.00	$167.00	$167.00
Purchase #2	$131.38	10.534%	$145.2196	$145.22	$145.20	$145.20
Purchase #3	$233.27	13.319%	$264.3392	$264.34	$264.35	$264.30
Purchase #4	$148.49	5.229%	$156.2545	$156.25	$156.25	$156.30
Purchase #5	$39.39	3.141%	$40.6272	$40.63	$40.65	$40.60
Purchase #6	$194.61	10.755%	$215.5403	$215.54	$215.55	$215.50
Purchase #7	$133.93	7.770%	$144.3364	$144.34	$144.35	$144.30
7 purchase totals =	$1,029.87		$1,133.3169	$1,133.32	$1,133.35	$1,133.20