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 $143.32   13.873%   $163.2028   $163.20   $163.20   $163.20  
  Purchase #2 $182.93   10.117%   $201.437   $201.44   $201.45   $201.40  
  Purchase #3 $73.56   4.119%   $76.5899   $76.59   $76.60   $76.60  
  Purchase #4 $146.72   4.253%   $152.96   $152.96   $152.95   $153.00  
  Purchase #5 $23.65   13.229%   $26.7787   $26.78   $26.80   $26.80  
  Purchase #6 $87.74   10.587%   $97.029   $97.03   $97.05   $97.00  
  Purchase #7 $225.35   7.486%   $242.2197   $242.22   $242.20   $242.20  
  7 purchase totals = $883.27       $960.2171   $960.22   $960.25   $960.20