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 $225.93   8.202%   $244.4608   $244.46   $244.45   $244.50  
  Purchase #2 $222.35   5.801%   $235.2485   $235.25   $235.25   $235.20  
  Purchase #3 $59.37   4.437%   $62.0042   $62.00   $62.00   $62.00  
  Purchase #4 $240.92   3.596%   $249.5835   $249.58   $249.60   $249.60  
  Purchase #5 $157.75   4.395%   $164.6831   $164.68   $164.70   $164.70  
  Purchase #6 $219.62   12.419%   $246.8946   $246.89   $246.90   $246.90  
  Purchase #7 $152.68   12.578%   $171.8841   $171.88   $171.90   $171.90  
  7 purchase totals = $1,278.62       $1,374.7588   $1,374.74   $1,374.80   $1,374.80