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 $58.81   13.834%   $66.9458   $66.95   $66.95   $66.90  
  Purchase #2 $74.80   8.599%   $81.2321   $81.23   $81.25   $81.20  
  Purchase #3 $104.61   5.400%   $110.2589   $110.26   $110.25   $110.30  
  Purchase #4 $175.95   6.284%   $187.0067   $187.01   $187.00   $187.00  
  Purchase #5 $27.87   9.115%   $30.4104   $30.41   $30.40   $30.40  
  Purchase #6 $211.88   8.118%   $229.0804   $229.08   $229.10   $229.10  
  Purchase #7 $205.44   4.596%   $214.882   $214.88   $214.90   $214.90  
  7 purchase totals = $859.36       $919.8163   $919.82   $919.85   $919.80