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 $231.88   3.366%   $239.6851   $239.69   $239.70   $239.70  
  Purchase #2 $56.66   6.855%   $60.544   $60.54   $60.55   $60.50  
  Purchase #3 $162.73   8.747%   $176.964   $176.96   $176.95   $177.00  
  Purchase #4 $59.69   6.412%   $63.5173   $63.52   $63.50   $63.50  
  Purchase #5 $133.57   13.658%   $151.813   $151.81   $151.80   $151.80  
  Purchase #6 $149.56   9.212%   $163.3375   $163.34   $163.35   $163.30  
  Purchase #7 $91.58   3.725%   $94.9914   $94.99   $95.00   $95.00  
  7 purchase totals = $885.67       $950.8523   $950.85   $950.85   $950.80