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 $57.93   13.398%   $65.6915   $65.69   $65.70   $65.70  
  Purchase #2 $210.96   4.573%   $220.6072   $220.61   $220.60   $220.60  
  Purchase #3 $8.84   8.569%   $9.5975   $9.60   $9.60   $9.60  
  Purchase #4 $52.46   5.113%   $55.1423   $55.14   $55.15   $55.10  
  Purchase #5 $164.56   8.182%   $178.0243   $178.02   $178.00   $178.00  
  Purchase #6 $186.56   7.425%   $200.4121   $200.41   $200.40   $200.40  
  Purchase #7 $196.98   4.531%   $205.9052   $205.91   $205.90   $205.90  
  7 purchase totals = $878.29       $935.3801   $935.38   $935.35   $935.30