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 $74.28   5.587%   $78.43   $78.43   $78.45   $78.40  
  Purchase #2 $234.78   5.480%   $247.6459   $247.65   $247.65   $247.60  
  Purchase #3 $69.40   9.755%   $76.17   $76.17   $76.15   $76.20  
  Purchase #4 $153.37   6.632%   $163.5415   $163.54   $163.55   $163.50  
  Purchase #5 $24.48   4.522%   $25.587   $25.59   $25.60   $25.60  
  Purchase #6 $230.32   6.435%   $245.1411   $245.14   $245.15   $245.10  
  Purchase #7 $188.47   7.545%   $202.6901   $202.69   $202.70   $202.70  
  7 purchase totals = $975.10       $1,039.2056   $1,039.21   $1,039.25   $1,039.10