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 $213.96   4.470%   $223.524   $223.52   $223.50   $223.50  
  Purchase #2 $241.54   5.680%   $255.2595   $255.26   $255.25   $255.30  
  Purchase #3 $93.46   11.680%   $104.3761   $104.38   $104.40   $104.40  
  Purchase #4 $58.68   6.561%   $62.53   $62.53   $62.55   $62.50  
  Purchase #5 $109.93   11.389%   $122.4499   $122.45   $122.45   $122.40  
  Purchase #6 $186.35   8.611%   $202.3966   $202.40   $202.40   $202.40  
  Purchase #7 $78.60   10.269%   $86.6714   $86.67   $86.65   $86.70  
  7 purchase totals = $982.52       $1,057.2075   $1,057.21   $1,057.20   $1,057.20