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 $51.36   6.529%   $54.7133   $54.71   $54.70   $54.70  
  Purchase #2 $55.26   10.835%   $61.2474   $61.25   $61.25   $61.20  
  Purchase #3 $94.30   10.830%   $104.5127   $104.51   $104.50   $104.50  
  Purchase #4 $149.65   8.278%   $162.038   $162.04   $162.05   $162.00  
  Purchase #5 $80.46   5.338%   $84.755   $84.76   $84.75   $84.80  
  Purchase #6 $26.65   3.555%   $27.5974   $27.60   $27.60   $27.60  
  Purchase #7 $222.35   6.208%   $236.1535   $236.15   $236.15   $236.20  
  7 purchase totals = $680.03       $731.0173   $731.02   $731.00   $731.00