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 $238.92   6.273%   $253.9075   $253.91   $253.90   $253.90  
  Purchase #2 $147.52   3.522%   $152.7157   $152.72   $152.70   $152.70  
  Purchase #3 $68.55   13.854%   $78.0469   $78.05   $78.05   $78.00  
  Purchase #4 $147.78   10.238%   $162.9097   $162.91   $162.90   $162.90  
  Purchase #5 $237.39   13.473%   $269.3736   $269.37   $269.35   $269.40  
  Purchase #6 $8.54   12.676%   $9.6225   $9.62   $9.60   $9.60  
  Purchase #7 $208.95   11.622%   $233.2342   $233.23   $233.25   $233.20  
  7 purchase totals = $1,057.65       $1,159.8101   $1,159.81   $1,159.75   $1,159.70