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 $185.61   10.727%   $205.5204   $205.52   $205.50   $205.50  
  Purchase #2 $153.71   7.692%   $165.5334   $165.53   $165.55   $165.50  
  Purchase #3 $41.42   7.613%   $44.5733   $44.57   $44.55   $44.60  
  Purchase #4 $50.60   13.172%   $57.265   $57.27   $57.25   $57.30  
  Purchase #5 $8.54   6.785%   $9.1194   $9.12   $9.10   $9.10  
  Purchase #6 $193.54   5.759%   $204.686   $204.69   $204.70   $204.70  
  Purchase #7 $46.69   4.717%   $48.8924   $48.89   $48.90   $48.90  
  7 purchase totals = $680.11       $735.5899   $735.59   $735.55   $735.60