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 $135.97   5.836%   $143.9052   $143.91   $143.90   $143.90  
  Purchase #2 $117.78   8.442%   $127.723   $127.72   $127.70   $127.70  
  Purchase #3 $59.60   8.641%   $64.75   $64.75   $64.75   $64.80  
  Purchase #4 $236.99   4.853%   $248.4911   $248.49   $248.50   $248.50  
  Purchase #5 $122.54   11.573%   $136.7216   $136.72   $136.70   $136.70  
  Purchase #6 $183.72   5.567%   $193.9477   $193.95   $193.95   $193.90  
  Purchase #7 $128.30   5.239%   $135.0216   $135.02   $135.00   $135.00  
  7 purchase totals = $984.90       $1,050.5602   $1,050.56   $1,050.50   $1,050.50