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 $197.40   13.731%   $224.505   $224.51   $224.50   $224.50  
  Purchase #2 $32.93   12.172%   $36.9382   $36.94   $36.95   $36.90  
  Purchase #3 $235.85   13.504%   $267.6992   $267.70   $267.70   $267.70  
  Purchase #4 $102.55   6.639%   $109.3583   $109.36   $109.35   $109.40  
  Purchase #5 $99.38   13.779%   $113.0736   $113.07   $113.05   $113.10  
  Purchase #6 $23.46   4.336%   $24.4772   $24.48   $24.50   $24.50  
  Purchase #7 $249.72   4.840%   $261.8064   $261.81   $261.80   $261.80  
  7 purchase totals = $941.29       $1,037.8579   $1,037.87   $1,037.85   $1,037.90