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 $126.92   6.332%   $134.9566   $134.96   $134.95   $135.00  
  Purchase #2 $249.77   11.587%   $278.7108   $278.71   $278.70   $278.70  
  Purchase #3 $233.73   7.155%   $250.4534   $250.45   $250.45   $250.50  
  Purchase #4 $112.31   4.200%   $117.027   $117.03   $117.05   $117.00  
  Purchase #5 $80.54   8.134%   $87.0911   $87.09   $87.10   $87.10  
  Purchase #6 $41.39   12.529%   $46.5758   $46.58   $46.60   $46.60  
  Purchase #7 $237.34   4.578%   $248.2054   $248.21   $248.20   $248.20  
  7 purchase totals = $1,082.00       $1,163.0201   $1,163.03   $1,163.05   $1,163.10