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 $239.80   11.360%   $267.0413   $267.04   $267.05   $267.00  
  Purchase #2 $77.55   12.226%   $87.0313   $87.03   $87.05   $87.00  
  Purchase #3 $154.35   6.283%   $164.0478   $164.05   $164.05   $164.00  
  Purchase #4 $55.72   8.127%   $60.2484   $60.25   $60.25   $60.20  
  Purchase #5 $59.47   6.696%   $63.4521   $63.45   $63.45   $63.50  
  Purchase #6 $99.92   4.577%   $104.4933   $104.49   $104.50   $104.50  
  Purchase #7 $27.26   4.813%   $28.572   $28.57   $28.55   $28.60  
  7 purchase totals = $714.07       $774.8862   $774.88   $774.90   $774.80