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 $172.92   8.283%   $187.243   $187.24   $187.25   $187.20  
  Purchase #2 $171.28   3.135%   $176.6496   $176.65   $176.65   $176.60  
  Purchase #3 $75.86   12.854%   $85.611   $85.61   $85.60   $85.60  
  Purchase #4 $227.64   6.712%   $242.9192   $242.92   $242.90   $242.90  
  Purchase #5 $104.95   12.624%   $118.1989   $118.20   $118.20   $118.20  
  Purchase #6 $203.90   7.722%   $219.6452   $219.65   $219.65   $219.60  
  Purchase #7 $248.54   12.326%   $279.175   $279.18   $279.20   $279.20  
  7 purchase totals = $1,205.09       $1,309.4419   $1,309.45   $1,309.45   $1,309.30