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	$37.60	13.150%	$42.5444	$42.54	$42.55	$42.50
Purchase #2	$77.67	4.185%	$80.9205	$80.92	$80.90	$80.90
Purchase #3	$205.50	3.803%	$213.3152	$213.32	$213.30	$213.30
Purchase #4	$94.83	8.830%	$103.2035	$103.20	$103.20	$103.20
Purchase #5	$162.72	8.697%	$176.8718	$176.87	$176.85	$176.90
Purchase #6	$150.45	12.806%	$169.7166	$169.72	$169.70	$169.70
Purchase #7	$60.90	8.261%	$65.9309	$65.93	$65.95	$65.90
7 purchase totals =	$789.67		$852.5029	$852.50	$852.45	$852.40