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 $61.99   10.705%   $68.626   $68.63   $68.65   $68.60  
  Purchase #2 $134.72   5.188%   $141.7093   $141.71   $141.70   $141.70  
  Purchase #3 $198.40   13.129%   $224.4479   $224.45   $224.45   $224.40  
  Purchase #4 $212.91   12.761%   $240.0794   $240.08   $240.10   $240.10  
  Purchase #5 $29.85   11.660%   $33.3305   $33.33   $33.35   $33.30  
  Purchase #6 $232.40   12.616%   $261.7196   $261.72   $261.70   $261.70  
  Purchase #7 $30.71   6.563%   $32.7255   $32.73   $32.75   $32.70  
  7 purchase totals = $900.98       $1,002.6382   $1,002.65   $1,002.70   $1,002.50