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 $246.82   5.739%   $260.985   $260.99   $261.00   $261.00  
  Purchase #2 $65.55   13.268%   $74.2472   $74.25   $74.25   $74.20  
  Purchase #3 $124.93   9.746%   $137.1057   $137.11   $137.10   $137.10  
  Purchase #4 $128.50   6.802%   $137.2406   $137.24   $137.25   $137.20  
  Purchase #5 $81.66   7.273%   $87.5991   $87.60   $87.60   $87.60  
  Purchase #6 $239.32   7.762%   $257.896   $257.90   $257.90   $257.90  
  Purchase #7 $72.59   11.410%   $80.8725   $80.87   $80.85   $80.90  
  7 purchase totals = $959.37       $1,035.9461   $1,035.96   $1,035.95   $1,035.90