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 $177.33   13.348%   $201   $201.00   $201.00   $201.00  
  Purchase #2 $143.55   8.142%   $155.2378   $155.24   $155.25   $155.20  
  Purchase #3 $56.87   6.744%   $60.7053   $60.71   $60.70   $60.70  
  Purchase #4 $200.68   4.567%   $209.8451   $209.85   $209.85   $209.80  
  Purchase #5 $72.96   8.797%   $79.3783   $79.38   $79.40   $79.40  
  Purchase #6 $111.27   13.112%   $125.8597   $125.86   $125.85   $125.90  
  Purchase #7 $66.57   6.515%   $70.907   $70.91   $70.90   $70.90  
  7 purchase totals = $829.23       $902.9332   $902.95   $902.95   $902.90