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 $95.75   12.163%   $107.3961   $107.40   $107.40   $107.40  
  Purchase #2 $100.35   4.446%   $104.8116   $104.81   $104.80   $104.80  
  Purchase #3 $56.43   8.862%   $61.4308   $61.43   $61.45   $61.40  
  Purchase #4 $143.68   4.260%   $149.8008   $149.80   $149.80   $149.80  
  Purchase #5 $82.74   4.259%   $86.2639   $86.26   $86.25   $86.30  
  Purchase #6 $224.97   11.389%   $250.5918   $250.59   $250.60   $250.60  
  Purchase #7 $8.71   5.586%   $9.1965   $9.20   $9.20   $9.20  
  7 purchase totals = $712.63       $769.4915   $769.49   $769.50   $769.50