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 $54.70   12.189%   $61.3674   $61.37   $61.35   $61.40  
  Purchase #2 $15.58   7.124%   $16.6899   $16.69   $16.70   $16.70  
  Purchase #3 $35.88   7.721%   $38.6503   $38.65   $38.65   $38.70  
  Purchase #4 $249.77   3.548%   $258.6318   $258.63   $258.65   $258.60  
  Purchase #5 $234.59   11.328%   $261.1644   $261.16   $261.15   $261.20  
  Purchase #6 $79.96   11.421%   $89.0922   $89.09   $89.10   $89.10  
  Purchase #7 $216.93   12.445%   $243.9269   $243.93   $243.95   $243.90  
  7 purchase totals = $887.41       $969.5229   $969.52   $969.55   $969.60