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 $65.42   3.182%   $67.5017   $67.50   $67.50   $67.50  
  Purchase #2 $161.79   8.666%   $175.8107   $175.81   $175.80   $175.80  
  Purchase #3 $69.89   8.150%   $75.586   $75.59   $75.60   $75.60  
  Purchase #4 $99.25   5.700%   $104.9073   $104.91   $104.90   $104.90  
  Purchase #5 $51.57   8.536%   $55.972   $55.97   $55.95   $56.00  
  Purchase #6 $60.53   5.390%   $63.7926   $63.79   $63.80   $63.80  
  Purchase #7 $130.73   10.770%   $144.8096   $144.81   $144.80   $144.80  
  7 purchase totals = $639.18       $688.3799   $688.38   $688.35   $688.40