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 $98.95   5.157%   $104.0529   $104.05   $104.05   $104.10  
  Purchase #2 $175.44   10.438%   $193.7524   $193.75   $193.75   $193.80  
  Purchase #3 $61.50   7.756%   $66.2699   $66.27   $66.25   $66.30  
  Purchase #4 $238.27   8.347%   $258.1584   $258.16   $258.15   $258.20  
  Purchase #5 $233.39   5.687%   $246.6629   $246.66   $246.65   $246.70  
  Purchase #6 $65.74   6.871%   $70.257   $70.26   $70.25   $70.30  
  Purchase #7 $10.30   8.732%   $11.1994   $11.20   $11.20   $11.20  
  7 purchase totals = $883.59       $950.3529   $950.35   $950.30   $950.60