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 $156.28   4.764%   $163.7252   $163.73   $163.75   $163.70  
  Purchase #2 $80.91   7.170%   $86.7112   $86.71   $86.70   $86.70  
  Purchase #3 $216.61   5.623%   $228.79   $228.79   $228.80   $228.80  
  Purchase #4 $155.76   4.807%   $163.2474   $163.25   $163.25   $163.20  
  Purchase #5 $77.69   5.706%   $82.123   $82.12   $82.10   $82.10  
  Purchase #6 $11.69   11.566%   $13.0421   $13.04   $13.05   $13.00  
  Purchase #7 $247.53   4.346%   $258.2877   $258.29   $258.30   $258.30  
  7 purchase totals = $946.47       $995.9266   $995.93   $995.95   $995.80