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 $32.62   9.176%   $35.6132   $35.61   $35.60   $35.60  
  Purchase #2 $226.48   12.785%   $255.4355   $255.44   $255.45   $255.40  
  Purchase #3 $103.34   6.225%   $109.7729   $109.77   $109.75   $109.80  
  Purchase #4 $187.66   8.596%   $203.7913   $203.79   $203.80   $203.80  
  Purchase #5 $107.67   5.871%   $113.9913   $113.99   $114.00   $114.00  
  Purchase #6 $202.81   8.416%   $219.8785   $219.88   $219.90   $219.90  
  Purchase #7 $134.39   9.478%   $147.1275   $147.13   $147.15   $147.10  
  7 purchase totals = $994.97       $1,085.6102   $1,085.61   $1,085.65   $1,085.60