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 $164.70   10.721%   $182.3575   $182.36   $182.35   $182.40  
  Purchase #2 $14.44   6.151%   $15.3282   $15.33   $15.35   $15.30  
  Purchase #3 $250.91   10.397%   $276.9971   $277.00   $277.00   $277.00  
  Purchase #4 $25.81   13.692%   $29.3439   $29.34   $29.35   $29.30  
  Purchase #5 $186.78   3.555%   $193.42   $193.42   $193.40   $193.40  
  Purchase #6 $183.31   10.558%   $202.6639   $202.66   $202.65   $202.70  
  Purchase #7 $131.36   5.215%   $138.2104   $138.21   $138.20   $138.20  
  7 purchase totals = $957.31       $1,038.3210   $1,038.32   $1,038.30   $1,038.30