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	$153.79	8.811%	$167.3404	$167.34	$167.35	$167.30
Purchase #2	$80.96	12.129%	$90.7796	$90.78	$90.80	$90.80
Purchase #3	$138.61	12.604%	$156.0804	$156.08	$156.10	$156.10
Purchase #4	$11.73	6.215%	$12.459	$12.46	$12.45	$12.50
Purchase #5	$171.62	13.497%	$194.7836	$194.78	$194.80	$194.80
Purchase #6	$123.64	13.866%	$140.7839	$140.78	$140.80	$140.80
Purchase #7	$21.74	13.423%	$24.6582	$24.66	$24.65	$24.70
7 purchase totals =	$702.09		$786.8851	$786.88	$786.95	$787.00