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 $97.41   5.804%   $103.0637   $103.06   $103.05   $103.10  
  Purchase #2 $49.65   13.659%   $56.4317   $56.43   $56.45   $56.40  
  Purchase #3 $20.59   7.575%   $22.1497   $22.15   $22.15   $22.10  
  Purchase #4 $53.45   9.802%   $58.6892   $58.69   $58.70   $58.70  
  Purchase #5 $199.73   11.558%   $222.8148   $222.81   $222.80   $222.80  
  Purchase #6 $171.73   3.825%   $178.2987   $178.30   $178.30   $178.30  
  Purchase #7 $138.32   5.287%   $145.633   $145.63   $145.65   $145.60  
  7 purchase totals = $730.88       $787.0808   $787.07   $787.10   $787.00