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 $242.81   10.354%   $267.9505   $267.95   $267.95   $268.00  
  Purchase #2 $48.62   10.794%   $53.868   $53.87   $53.85   $53.90  
  Purchase #3 $200.90   11.752%   $224.5098   $224.51   $224.50   $224.50  
  Purchase #4 $80.81   10.684%   $89.4437   $89.44   $89.45   $89.40  
  Purchase #5 $102.97   9.819%   $113.0806   $113.08   $113.10   $113.10  
  Purchase #6 $209.64   4.554%   $219.187   $219.19   $219.20   $219.20  
  Purchase #7 $122.69   10.175%   $135.1737   $135.17   $135.15   $135.20  
  7 purchase totals = $1,008.44       $1,103.2133   $1,103.21   $1,103.20   $1,103.30