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 $61.32   8.357%   $66.4445   $66.44   $66.45   $66.40  
  Purchase #2 $244.65   6.473%   $260.4862   $260.49   $260.50   $260.50  
  Purchase #3 $125.62   4.703%   $131.5279   $131.53   $131.55   $131.50  
  Purchase #4 $52.75   11.622%   $58.8806   $58.88   $58.90   $58.90  
  Purchase #5 $82.87   13.322%   $93.9099   $93.91   $93.90   $93.90  
  Purchase #6 $245.52   6.364%   $261.1449   $261.14   $261.15   $261.10  
  Purchase #7 $157.76   10.227%   $173.8941   $173.89   $173.90   $173.90  
  7 purchase totals = $970.49       $1,046.2881   $1,046.28   $1,046.35   $1,046.20