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	$201.30	9.451%	$220.3249	$220.32	$220.30	$220.30
Purchase #2	$50.43	4.820%	$52.8607	$52.86	$52.85	$52.90
Purchase #3	$85.98	7.871%	$92.7475	$92.75	$92.75	$92.70
Purchase #4	$49.72	12.556%	$55.9628	$55.96	$55.95	$56.00
Purchase #5	$27.41	5.184%	$28.8309	$28.83	$28.85	$28.80
Purchase #6	$13.25	12.387%	$14.8913	$14.89	$14.90	$14.90
Purchase #7	$213.32	13.415%	$241.9369	$241.94	$241.95	$241.90
7 purchase totals =	$641.41		$707.5550	$707.55	$707.55	$707.50