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 $51.98   8.806%   $56.5574   $56.56   $56.55   $56.60  
  Purchase #2 $102.94   10.668%   $113.9216   $113.92   $113.90   $113.90  
  Purchase #3 $136.97   13.544%   $155.5212   $155.52   $155.50   $155.50  
  Purchase #4 $25.26   5.433%   $26.6324   $26.63   $26.65   $26.60  
  Purchase #5 $212.33   5.537%   $224.0867   $224.09   $224.10   $224.10  
  Purchase #6 $93.54   5.402%   $98.593   $98.59   $98.60   $98.60  
  Purchase #7 $165.41   5.213%   $174.0328   $174.03   $174.05   $174.00  
  7 purchase totals = $788.43       $849.3451   $849.34   $849.35   $849.30