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 $142.69   10.482%   $157.6468   $157.65   $157.65   $157.60  
  Purchase #2 $152.94   6.359%   $162.6655   $162.67   $162.65   $162.70  
  Purchase #3 $163.34   5.482%   $172.2943   $172.29   $172.30   $172.30  
  Purchase #4 $7.75   6.848%   $8.2807   $8.28   $8.30   $8.30  
  Purchase #5 $205.30   7.496%   $220.6893   $220.69   $220.70   $220.70  
  Purchase #6 $100.68   13.781%   $114.5547   $114.55   $114.55   $114.60  
  Purchase #7 $182.58   9.855%   $200.5733   $200.57   $200.55   $200.60  
  7 purchase totals = $955.28       $1,036.7046   $1,036.70   $1,036.70   $1,036.80