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 $186.75   12.414%   $209.9331   $209.93   $209.95   $209.90  
  Purchase #2 $67.30   3.804%   $69.8601   $69.86   $69.85   $69.90  
  Purchase #3 $237.64   5.483%   $250.6698   $250.67   $250.65   $250.70  
  Purchase #4 $93.41   5.123%   $98.1954   $98.20   $98.20   $98.20  
  Purchase #5 $195.45   4.626%   $204.4915   $204.49   $204.50   $204.50  
  Purchase #6 $238.79   9.710%   $261.9765   $261.98   $262.00   $262.00  
  Purchase #7 $113.82   3.428%   $117.7217   $117.72   $117.70   $117.70  
  7 purchase totals = $1,133.16       $1,212.8481   $1,212.85   $1,212.85   $1,212.90