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	$227.39	12.745%	$256.3709	$256.37	$256.35	$256.40
Purchase #2	$36.97	8.421%	$40.0832	$40.08	$40.10	$40.10
Purchase #3	$90.59	4.124%	$94.3259	$94.33	$94.35	$94.30
Purchase #4	$186.56	3.261%	$192.6437	$192.64	$192.65	$192.60
Purchase #5	$117.51	9.188%	$128.3068	$128.31	$128.30	$128.30
Purchase #6	$240.52	13.648%	$273.3462	$273.35	$273.35	$273.30
Purchase #7	$196.57	4.748%	$205.9031	$205.90	$205.90	$205.90
7 purchase totals =	$1,096.11		$1,190.9798	$1,190.98	$1,191.00	$1,190.90