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 $117.51   8.307%   $127.2716   $127.27   $127.25   $127.30  
  Purchase #2 $242.41   7.749%   $261.1944   $261.19   $261.20   $261.20  
  Purchase #3 $88.92   9.671%   $97.5195   $97.52   $97.50   $97.50  
  Purchase #4 $82.66   4.222%   $86.1499   $86.15   $86.15   $86.10  
  Purchase #5 $207.98   10.634%   $230.0966   $230.10   $230.10   $230.10  
  Purchase #6 $166.89   8.221%   $180.61   $180.61   $180.60   $180.60  
  Purchase #7 $51.92   13.241%   $58.7947   $58.79   $58.80   $58.80  
  7 purchase totals = $958.29       $1,041.6367   $1,041.63   $1,041.60   $1,041.60