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 $125.57   7.164%   $134.5658   $134.57   $134.55   $134.60  
  Purchase #2 $211.42   11.838%   $236.4479   $236.45   $236.45   $236.40  
  Purchase #3 $78.42   12.248%   $88.0249   $88.02   $88.00   $88.00  
  Purchase #4 $171.73   3.289%   $177.3782   $177.38   $177.40   $177.40  
  Purchase #5 $219.30   6.256%   $233.0194   $233.02   $233.00   $233.00  
  Purchase #6 $250.94   13.379%   $284.5133   $284.51   $284.50   $284.50  
  Purchase #7 $163.85   5.212%   $172.3899   $172.39   $172.40   $172.40  
  7 purchase totals = $1,221.23       $1,326.3394   $1,326.34   $1,326.30   $1,326.30