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 $213.37   13.624%   $242.4395   $242.44   $242.45   $242.40  
  Purchase #2 $59.95   13.457%   $68.0175   $68.02   $68.00   $68.00  
  Purchase #3 $92.58   13.214%   $104.8135   $104.81   $104.80   $104.80  
  Purchase #4 $24.87   7.353%   $26.6987   $26.70   $26.70   $26.70  
  Purchase #5 $223.66   9.216%   $244.2725   $244.27   $244.25   $244.30  
  Purchase #6 $116.35   7.354%   $124.9064   $124.91   $124.90   $124.90  
  Purchase #7 $233.68   9.738%   $256.4358   $256.44   $256.45   $256.40  
  7 purchase totals = $964.46       $1,067.5839   $1,067.59   $1,067.55   $1,067.50