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 $57.46   13.648%   $65.3021   $65.30   $65.30   $65.30  
  Purchase #2 $92.76   8.406%   $100.5574   $100.56   $100.55   $100.60  
  Purchase #3 $246.71   5.583%   $260.4838   $260.48   $260.50   $260.50  
  Purchase #4 $210.45   6.498%   $224.125   $224.13   $224.15   $224.10  
  Purchase #5 $13.56   4.516%   $14.1724   $14.17   $14.15   $14.20  
  Purchase #6 $192.38   3.648%   $199.398   $199.40   $199.40   $199.40  
  Purchase #7 $186.30   13.778%   $211.9684   $211.97   $211.95   $212.00  
  7 purchase totals = $999.62       $1,076.0071   $1,076.01   $1,076.00   $1,076.10