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 $201.76   8.682%   $219.2768   $219.28   $219.30   $219.30  
  Purchase #2 $52.93   3.420%   $54.7402   $54.74   $54.75   $54.70  
  Purchase #3 $239.69   5.874%   $253.7694   $253.77   $253.75   $253.80  
  Purchase #4 $201.88   8.797%   $219.6394   $219.64   $219.65   $219.60  
  Purchase #5 $219.53   13.260%   $248.6397   $248.64   $248.65   $248.60  
  Purchase #6 $210.86   10.702%   $233.4262   $233.43   $233.45   $233.40  
  Purchase #7 $190.53   4.126%   $198.3913   $198.39   $198.40   $198.40  
  7 purchase totals = $1,317.18       $1,427.8830   $1,427.89   $1,427.95   $1,427.80