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 $225.81   11.826%   $252.5143   $252.51   $252.50   $252.50  
  Purchase #2 $187.25   13.691%   $212.8864   $212.89   $212.90   $212.90  
  Purchase #3 $151.79   8.484%   $164.6679   $164.67   $164.65   $164.70  
  Purchase #4 $239.35   6.376%   $254.611   $254.61   $254.60   $254.60  
  Purchase #5 $78.60   10.133%   $86.5645   $86.56   $86.55   $86.60  
  Purchase #6 $200.96   6.250%   $213.52   $213.52   $213.50   $213.50  
  Purchase #7 $133.37   4.588%   $139.489   $139.49   $139.50   $139.50  
  7 purchase totals = $1,217.13       $1,324.2531   $1,324.25   $1,324.20   $1,324.30