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	$32.83	13.529%	$37.2716	$37.27	$37.25	$37.30
Purchase #2	$47.86	7.116%	$51.2657	$51.27	$51.25	$51.30
Purchase #3	$241.47	12.830%	$272.4506	$272.45	$272.45	$272.50
Purchase #4	$150.30	12.785%	$169.5159	$169.52	$169.50	$169.50
Purchase #5	$161.82	6.204%	$171.8593	$171.86	$171.85	$171.90
Purchase #6	$148.32	12.797%	$167.3005	$167.30	$167.30	$167.30
Purchase #7	$177.52	8.134%	$191.9595	$191.96	$191.95	$192.00
7 purchase totals =	$960.12		$1,061.6231	$1,061.63	$1,061.55	$1,061.80