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 $32.92   10.469%   $36.3664   $36.37   $36.35   $36.40  
  Purchase #2 $154.63   7.823%   $166.7267   $166.73   $166.75   $166.70  
  Purchase #3 $177.49   11.574%   $198.0327   $198.03   $198.05   $198.00  
  Purchase #4 $202.79   11.443%   $225.9953   $226.00   $226.00   $226.00  
  Purchase #5 $125.95   8.441%   $136.5814   $136.58   $136.60   $136.60  
  Purchase #6 $32.73   7.478%   $35.1775   $35.18   $35.20   $35.20  
  Purchase #7 $203.92   10.190%   $224.6994   $224.70   $224.70   $224.70  
  7 purchase totals = $930.43       $1,023.5794   $1,023.59   $1,023.65   $1,023.60