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 $229.37   11.741%   $256.3003   $256.30   $256.30   $256.30  
  Purchase #2 $108.48   13.227%   $122.8286   $122.83   $122.85   $122.80  
  Purchase #3 $54.57   11.684%   $60.946   $60.95   $60.95   $60.90  
  Purchase #4 $56.91   13.622%   $64.6623   $64.66   $64.65   $64.70  
  Purchase #5 $221.45   6.524%   $235.8974   $235.90   $235.90   $235.90  
  Purchase #6 $73.77   6.341%   $78.4478   $78.45   $78.45   $78.40  
  Purchase #7 $213.37   9.301%   $233.2155   $233.22   $233.20   $233.20  
  7 purchase totals = $957.92       $1,052.2979   $1,052.31   $1,052.30   $1,052.20