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 $74.61   10.793%   $82.6627   $82.66   $82.65   $82.70  
  Purchase #2 $24.52   8.147%   $26.5176   $26.52   $26.50   $26.50  
  Purchase #3 $186.78   12.332%   $209.8137   $209.81   $209.80   $209.80  
  Purchase #4 $35.45   11.228%   $39.4303   $39.43   $39.45   $39.40  
  Purchase #5 $83.59   12.272%   $93.8482   $93.85   $93.85   $93.80  
  Purchase #6 $207.38   13.442%   $235.256   $235.26   $235.25   $235.30  
  Purchase #7 $16.59   5.287%   $17.4671   $17.47   $17.45   $17.50  
  7 purchase totals = $628.92       $704.9956   $705.00   $704.95   $705.00