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 $237.54   11.788%   $265.5412   $265.54   $265.55   $265.50  
  Purchase #2 $223.59   11.773%   $249.9133   $249.91   $249.90   $249.90  
  Purchase #3 $86.32   13.465%   $97.943   $97.94   $97.95   $97.90  
  Purchase #4 $54.42   11.564%   $60.7131   $60.71   $60.70   $60.70  
  Purchase #5 $217.58   8.318%   $235.6783   $235.68   $235.70   $235.70  
  Purchase #6 $192.35   13.127%   $217.5998   $217.60   $217.60   $217.60  
  Purchase #7 $20.88   5.781%   $22.0871   $22.09   $22.10   $22.10  
  7 purchase totals = $1,032.68       $1,149.4758   $1,149.47   $1,149.50   $1,149.40