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 $190.64   7.303%   $204.5624   $204.56   $204.55   $204.60  
  Purchase #2 $248.27   8.562%   $269.5269   $269.53   $269.55   $269.50  
  Purchase #3 $113.83   8.713%   $123.748   $123.75   $123.75   $123.70  
  Purchase #4 $197.93   5.159%   $208.1412   $208.14   $208.15   $208.10  
  Purchase #5 $6.90   13.828%   $7.8541   $7.85   $7.85   $7.90  
  Purchase #6 $231.92   8.496%   $251.6239   $251.62   $251.60   $251.60  
  Purchase #7 $185.67   4.799%   $194.5803   $194.58   $194.60   $194.60  
  7 purchase totals = $1,175.16       $1,260.0368   $1,260.03   $1,260.05   $1,260.00