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 $233.54   5.378%   $246.0998   $246.10   $246.10   $246.10  
  Purchase #2 $41.58   7.391%   $44.6532   $44.65   $44.65   $44.70  
  Purchase #3 $104.35   9.418%   $114.1777   $114.18   $114.20   $114.20  
  Purchase #4 $142.71   7.601%   $153.5574   $153.56   $153.55   $153.60  
  Purchase #5 $85.81   13.517%   $97.4089   $97.41   $97.40   $97.40  
  Purchase #6 $158.26   4.188%   $164.8879   $164.89   $164.90   $164.90  
  Purchase #7 $231.98   6.157%   $246.263   $246.26   $246.25   $246.30  
  7 purchase totals = $998.23       $1,067.0479   $1,067.05   $1,067.05   $1,067.20