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 $249.41   7.473%   $268.0484   $268.05   $268.05   $268.00  
  Purchase #2 $210.73   6.593%   $224.6234   $224.62   $224.60   $224.60  
  Purchase #3 $123.69   11.280%   $137.6422   $137.64   $137.65   $137.60  
  Purchase #4 $173.60   10.404%   $191.6613   $191.66   $191.65   $191.70  
  Purchase #5 $57.83   11.560%   $64.5151   $64.52   $64.50   $64.50  
  Purchase #6 $163.48   8.701%   $177.7044   $177.70   $177.70   $177.70  
  Purchase #7 $205.26   8.238%   $222.1693   $222.17   $222.15   $222.20  
  7 purchase totals = $1,184.00       $1,286.3641   $1,286.36   $1,286.30   $1,286.30