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 $106.44   7.599%   $114.5284   $114.53   $114.55   $114.50  
  Purchase #2 $98.66   10.704%   $109.2206   $109.22   $109.20   $109.20  
  Purchase #3 $89.92   8.853%   $97.8806   $97.88   $97.90   $97.90  
  Purchase #4 $66.91   5.833%   $70.8129   $70.81   $70.80   $70.80  
  Purchase #5 $131.70   6.559%   $140.3382   $140.34   $140.35   $140.30  
  Purchase #6 $181.51   12.311%   $203.8557   $203.86   $203.85   $203.90  
  Purchase #7 $204.84   12.457%   $230.3569   $230.36   $230.35   $230.40  
  7 purchase totals = $879.98       $966.9933   $967.00   $967.00   $967.00