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 $101.95   11.498%   $113.6722   $113.67   $113.65   $113.70  
  Purchase #2 $235.78   12.755%   $265.8537   $265.85   $265.85   $265.90  
  Purchase #3 $246.73   10.492%   $272.6169   $272.62   $272.60   $272.60  
  Purchase #4 $170.60   3.414%   $176.4243   $176.42   $176.40   $176.40  
  Purchase #5 $54.77   5.207%   $57.6219   $57.62   $57.60   $57.60  
  Purchase #6 $228.53   11.866%   $255.6474   $255.65   $255.65   $255.60  
  Purchase #7 $171.70   9.437%   $187.9033   $187.90   $187.90   $187.90  
  7 purchase totals = $1,210.06       $1,329.7397   $1,329.73   $1,329.65   $1,329.70