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 $126.29   8.422%   $136.9261   $136.93   $136.95   $136.90  
  Purchase #2 $52.31   5.172%   $55.0155   $55.02   $55.00   $55.00  
  Purchase #3 $52.32   6.397%   $55.6669   $55.67   $55.65   $55.70  
  Purchase #4 $52.68   7.745%   $56.7601   $56.76   $56.75   $56.80  
  Purchase #5 $247.70   10.738%   $274.298   $274.30   $274.30   $274.30  
  Purchase #6 $232.44   7.759%   $250.475   $250.48   $250.50   $250.50  
  Purchase #7 $247.93   12.346%   $278.5394   $278.54   $278.55   $278.50  
  7 purchase totals = $1,011.67       $1,107.6810   $1,107.70   $1,107.70   $1,107.70