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 $84.56   10.401%   $93.3551   $93.36   $93.35   $93.40  
  Purchase #2 $25.54   3.855%   $26.5246   $26.52   $26.50   $26.50  
  Purchase #3 $232.57   12.536%   $261.725   $261.73   $261.75   $261.70  
  Purchase #4 $76.25   8.635%   $82.8342   $82.83   $82.85   $82.80  
  Purchase #5 $211.69   4.409%   $221.0234   $221.02   $221.00   $221.00  
  Purchase #6 $198.52   6.806%   $212.0313   $212.03   $212.05   $212.00  
  Purchase #7 $54.95   6.222%   $58.369   $58.37   $58.35   $58.40  
  7 purchase totals = $884.08       $955.8626   $955.86   $955.85   $955.80