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 $182.87   13.718%   $207.9561   $207.96   $207.95   $208.00  
  Purchase #2 $213.57   11.117%   $237.3126   $237.31   $237.30   $237.30  
  Purchase #3 $24.89   11.355%   $27.7163   $27.72   $27.70   $27.70  
  Purchase #4 $132.63   5.629%   $140.0957   $140.10   $140.10   $140.10  
  Purchase #5 $248.96   7.540%   $267.7316   $267.73   $267.75   $267.70  
  Purchase #6 $13.69   9.207%   $14.9504   $14.95   $14.95   $15.00  
  Purchase #7 $239.88   6.195%   $254.7406   $254.74   $254.75   $254.70  
  7 purchase totals = $1,056.49       $1,150.5033   $1,150.51   $1,150.50   $1,150.50