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 $23.58   10.643%   $26.0896   $26.09   $26.10   $26.10  
  Purchase #2 $75.59   11.538%   $84.3116   $84.31   $84.30   $84.30  
  Purchase #3 $50.99   9.673%   $55.9223   $55.92   $55.90   $55.90  
  Purchase #4 $220.73   4.777%   $231.2743   $231.27   $231.25   $231.30  
  Purchase #5 $152.43   10.593%   $168.5769   $168.58   $168.60   $168.60  
  Purchase #6 $248.64   11.743%   $277.8378   $277.84   $277.85   $277.80  
  Purchase #7 $16.25   10.243%   $17.9145   $17.91   $17.90   $17.90  
  7 purchase totals = $788.21       $861.9270   $861.92   $861.90   $861.90