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 $225.41   12.383%   $253.3225   $253.32   $253.30   $253.30  
  Purchase #2 $114.45   5.755%   $121.0366   $121.04   $121.05   $121.00  
  Purchase #3 $246.52   12.593%   $277.5643   $277.56   $277.55   $277.60  
  Purchase #4 $143.87   13.454%   $163.2263   $163.23   $163.25   $163.20  
  Purchase #5 $146.52   10.515%   $161.9266   $161.93   $161.95   $161.90  
  Purchase #6 $75.52   4.120%   $78.6314   $78.63   $78.65   $78.60  
  Purchase #7 $78.94   8.597%   $85.7265   $85.73   $85.75   $85.70  
  7 purchase totals = $1,031.23       $1,141.4342   $1,141.44   $1,141.50   $1,141.30