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 $191.65   8.264%   $207.488   $207.49   $207.50   $207.50  
  Purchase #2 $142.58   4.366%   $148.805   $148.81   $148.80   $148.80  
  Purchase #3 $231.36   6.603%   $246.6367   $246.64   $246.65   $246.60  
  Purchase #4 $61.93   4.786%   $64.894   $64.89   $64.90   $64.90  
  Purchase #5 $217.84   10.681%   $241.1075   $241.11   $241.10   $241.10  
  Purchase #6 $57.91   3.366%   $59.8593   $59.86   $59.85   $59.90  
  Purchase #7 $64.38   5.800%   $68.114   $68.11   $68.10   $68.10  
  7 purchase totals = $967.65       $1,036.9045   $1,036.91   $1,036.90   $1,036.90