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 $113.36   5.434%   $119.52   $119.52   $119.50   $119.50  
  Purchase #2 $159.46   5.461%   $168.1681   $168.17   $168.15   $168.20  
  Purchase #3 $129.86   4.838%   $136.1426   $136.14   $136.15   $136.10  
  Purchase #4 $225.70   4.461%   $235.7685   $235.77   $235.75   $235.80  
  Purchase #5 $73.52   6.393%   $78.2201   $78.22   $78.20   $78.20  
  Purchase #6 $25.59   4.439%   $26.7259   $26.73   $26.75   $26.70  
  Purchase #7 $16.52   11.679%   $18.4494   $18.45   $18.45   $18.40  
  7 purchase totals = $744.01       $782.9946   $783.00   $782.95   $782.90