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 $245.49   5.323%   $258.5574   $258.56   $258.55   $258.60  
  Purchase #2 $103.41   11.558%   $115.3621   $115.36   $115.35   $115.40  
  Purchase #3 $117.45   10.814%   $130.151   $130.15   $130.15   $130.20  
  Purchase #4 $71.44   5.343%   $75.257   $75.26   $75.25   $75.30  
  Purchase #5 $161.41   11.316%   $179.6752   $179.68   $179.70   $179.70  
  Purchase #6 $156.77   13.609%   $178.1048   $178.10   $178.10   $178.10  
  Purchase #7 $49.47   12.706%   $55.7557   $55.76   $55.75   $55.80  
  7 purchase totals = $905.44       $992.8632   $992.87   $992.85   $993.10