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 $84.31   10.265%   $92.9644   $92.96   $92.95   $93.00  
  Purchase #2 $214.27   8.602%   $232.7015   $232.70   $232.70   $232.70  
  Purchase #3 $234.65   6.176%   $249.142   $249.14   $249.15   $249.10  
  Purchase #4 $35.95   4.526%   $37.5771   $37.58   $37.60   $37.60  
  Purchase #5 $164.73   7.498%   $177.0815   $177.08   $177.10   $177.10  
  Purchase #6 $92.74   13.170%   $104.9539   $104.95   $104.95   $105.00  
  Purchase #7 $227.56   13.489%   $258.2556   $258.26   $258.25   $258.30  
  7 purchase totals = $1,054.21       $1,152.6760   $1,152.67   $1,152.70   $1,152.80