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 $168.93   11.616%   $188.5529   $188.55   $188.55   $188.60  
  Purchase #2 $95.61   7.266%   $102.557   $102.56   $102.55   $102.60  
  Purchase #3 $46.93   13.722%   $53.3697   $53.37   $53.35   $53.40  
  Purchase #4 $235.27   3.177%   $242.7445   $242.74   $242.75   $242.70  
  Purchase #5 $101.73   3.143%   $104.9274   $104.93   $104.95   $104.90  
  Purchase #6 $247.81   13.134%   $280.3574   $280.36   $280.35   $280.40  
  Purchase #7 $102.77   3.114%   $105.9703   $105.97   $105.95   $106.00  
  7 purchase totals = $999.05       $1,078.4792   $1,078.48   $1,078.45   $1,078.60