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 $23.94   9.867%   $26.3022   $26.30   $26.30   $26.30  
  Purchase #2 $131.45   9.319%   $143.6998   $143.70   $143.70   $143.70  
  Purchase #3 $112.90   6.274%   $119.9833   $119.98   $120.00   $120.00  
  Purchase #4 $75.39   3.498%   $78.0271   $78.03   $78.05   $78.00  
  Purchase #5 $78.51   9.586%   $86.036   $86.04   $86.05   $86.00  
  Purchase #6 $181.58   13.667%   $206.3965   $206.40   $206.40   $206.40  
  Purchase #7 $222.55   11.511%   $248.1677   $248.17   $248.15   $248.20  
  7 purchase totals = $826.32       $908.6126   $908.62   $908.65   $908.60