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 $200.85   6.383%   $213.6703   $213.67   $213.65   $213.70  
  Purchase #2 $186.71   8.108%   $201.8484   $201.85   $201.85   $201.80  
  Purchase #3 $239.39   9.384%   $261.8544   $261.85   $261.85   $261.90  
  Purchase #4 $57.40   6.168%   $60.9404   $60.94   $60.95   $60.90  
  Purchase #5 $76.45   12.356%   $85.8962   $85.90   $85.90   $85.90  
  Purchase #6 $157.58   11.326%   $175.4275   $175.43   $175.45   $175.40  
  Purchase #7 $167.47   4.605%   $175.182   $175.18   $175.20   $175.20  
  7 purchase totals = $1,085.85       $1,174.8192   $1,174.82   $1,174.85   $1,174.80