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 $166.78   10.666%   $184.5688   $184.57   $184.55   $184.60  
  Purchase #2 $26.39   4.303%   $27.5256   $27.53   $27.55   $27.50  
  Purchase #3 $163.90   5.355%   $172.6768   $172.68   $172.70   $172.70  
  Purchase #4 $92.90   12.152%   $104.1892   $104.19   $104.20   $104.20  
  Purchase #5 $168.26   7.529%   $180.9283   $180.93   $180.95   $180.90  
  Purchase #6 $201.53   12.738%   $227.2009   $227.20   $227.20   $227.20  
  Purchase #7 $127.86   12.674%   $144.065   $144.07   $144.05   $144.10  
  7 purchase totals = $947.62       $1,041.1546   $1,041.17   $1,041.20   $1,041.20