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 $197.73   5.289%   $208.1879   $208.19   $208.20   $208.20  
  Purchase #2 $163.53   10.690%   $181.0114   $181.01   $181.00   $181.00  
  Purchase #3 $175.34   6.554%   $186.8318   $186.83   $186.85   $186.80  
  Purchase #4 $114.79   12.141%   $128.7267   $128.73   $128.75   $128.70  
  Purchase #5 $141.84   11.412%   $158.0268   $158.03   $158.05   $158.00  
  Purchase #6 $31.93   8.586%   $34.6715   $34.67   $34.65   $34.70  
  Purchase #7 $115.27   8.640%   $125.2293   $125.23   $125.25   $125.20  
  7 purchase totals = $940.43       $1,022.6854   $1,022.69   $1,022.75   $1,022.60