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 $57.69   13.206%   $65.3085   $65.31   $65.30   $65.30  
  Purchase #2 $179.99   10.507%   $198.9015   $198.90   $198.90   $198.90  
  Purchase #3 $84.32   4.846%   $88.4061   $88.41   $88.40   $88.40  
  Purchase #4 $76.66   12.815%   $86.484   $86.48   $86.50   $86.50  
  Purchase #5 $222.30   12.698%   $250.5277   $250.53   $250.55   $250.50  
  Purchase #6 $108.54   12.230%   $121.8144   $121.81   $121.80   $121.80  
  Purchase #7 $210.67   6.135%   $223.5946   $223.59   $223.60   $223.60  
  7 purchase totals = $940.17       $1,035.0368   $1,035.03   $1,035.05   $1,035.00