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	$29.66	12.411%	$33.3411	$33.34	$33.35	$33.30
Purchase #2	$174.70	10.163%	$192.4548	$192.45	$192.45	$192.50
Purchase #3	$215.38	5.786%	$227.8419	$227.84	$227.85	$227.80
Purchase #4	$37.91	13.530%	$43.0392	$43.04	$43.05	$43.00
Purchase #5	$80.46	7.692%	$86.649	$86.65	$86.65	$86.60
Purchase #6	$80.26	12.180%	$90.0357	$90.04	$90.05	$90.00
Purchase #7	$97.30	5.174%	$102.3343	$102.33	$102.35	$102.30
7 purchase totals =	$715.67		$775.6960	$775.69	$775.75	$775.50