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	$88.30	3.423%	$91.3225	$91.32	$91.30	$91.30
Purchase #2	$13.71	9.739%	$15.0452	$15.05	$15.05	$15.00
Purchase #3	$152.59	3.853%	$158.4693	$158.47	$158.45	$158.50
Purchase #4	$208.72	5.409%	$220.0097	$220.01	$220.00	$220.00
Purchase #5	$39.52	4.444%	$41.2763	$41.28	$41.30	$41.30
Purchase #6	$241.54	12.338%	$271.3412	$271.34	$271.35	$271.30
Purchase #7	$100.47	8.867%	$109.3787	$109.38	$109.40	$109.40
7 purchase totals =	$844.85		$906.8429	$906.85	$906.85	$906.80