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 $228.45   3.426%   $236.2767   $236.28   $236.30   $236.30  
  Purchase #2 $97.92   5.813%   $103.6121   $103.61   $103.60   $103.60  
  Purchase #3 $155.39   4.595%   $162.5302   $162.53   $162.55   $162.50  
  Purchase #4 $243.62   12.778%   $274.7498   $274.75   $274.75   $274.70  
  Purchase #5 $95.40   8.381%   $103.3955   $103.40   $103.40   $103.40  
  Purchase #6 $122.67   3.266%   $126.6764   $126.68   $126.70   $126.70  
  Purchase #7 $217.67   13.313%   $246.6484   $246.65   $246.65   $246.60  
  7 purchase totals = $1,161.12       $1,253.8891   $1,253.90   $1,253.95   $1,253.80