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 $130.63   6.755%   $139.4541   $139.45   $139.45   $139.50  
  Purchase #2 $198.58   5.320%   $209.1445   $209.14   $209.15   $209.10  
  Purchase #3 $115.84   4.831%   $121.4362   $121.44   $121.45   $121.40  
  Purchase #4 $179.55   10.243%   $197.9413   $197.94   $197.95   $197.90  
  Purchase #5 $8.43   6.342%   $8.9646   $8.96   $8.95   $9.00  
  Purchase #6 $239.96   13.448%   $272.2298   $272.23   $272.25   $272.20  
  Purchase #7 $11.60   12.379%   $13.036   $13.04   $13.05   $13.00  
  7 purchase totals = $884.59       $962.2065   $962.20   $962.25   $962.10