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 $250.61   7.314%   $268.9396   $268.94   $268.95   $268.90  
  Purchase #2 $209.26   6.747%   $223.3788   $223.38   $223.40   $223.40  
  Purchase #3 $149.79   8.749%   $162.8951   $162.90   $162.90   $162.90  
  Purchase #4 $138.76   13.183%   $157.0527   $157.05   $157.05   $157.10  
  Purchase #5 $23.25   7.431%   $24.9777   $24.98   $25.00   $25.00  
  Purchase #6 $164.97   4.354%   $172.1528   $172.15   $172.15   $172.20  
  Purchase #7 $46.55   5.227%   $48.9832   $48.98   $49.00   $49.00  
  7 purchase totals = $983.19       $1,058.3799   $1,058.38   $1,058.45   $1,058.50