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 $76.67   11.155%   $85.2225   $85.22   $85.20   $85.20  
  Purchase #2 $26.89   6.729%   $28.6994   $28.70   $28.70   $28.70  
  Purchase #3 $114.69   3.391%   $118.5791   $118.58   $118.60   $118.60  
  Purchase #4 $239.59   4.121%   $249.4635   $249.46   $249.45   $249.50  
  Purchase #5 $15.29   13.410%   $17.3404   $17.34   $17.35   $17.30  
  Purchase #6 $81.50   7.134%   $87.3142   $87.31   $87.30   $87.30  
  Purchase #7 $170.55   5.175%   $179.376   $179.38   $179.40   $179.40  
  7 purchase totals = $725.18       $765.9951   $765.99   $766.00   $766.00