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 $204.92   10.803%   $227.0575   $227.06   $227.05   $227.10  
  Purchase #2 $196.87   11.621%   $219.7483   $219.75   $219.75   $219.70  
  Purchase #3 $28.81   5.558%   $30.4113   $30.41   $30.40   $30.40  
  Purchase #4 $233.93   3.358%   $241.7854   $241.79   $241.80   $241.80  
  Purchase #5 $210.31   11.776%   $235.0761   $235.08   $235.10   $235.10  
  Purchase #6 $50.28   11.872%   $56.2492   $56.25   $56.25   $56.20  
  Purchase #7 $133.51   11.116%   $148.351   $148.35   $148.35   $148.40  
  7 purchase totals = $1,058.63       $1,158.6788   $1,158.69   $1,158.70   $1,158.70