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 $32.59   13.607%   $37.0245   $37.02   $37.00   $37.00  
  Purchase #2 $85.95   6.662%   $91.676   $91.68   $91.70   $91.70  
  Purchase #3 $14.32   10.768%   $15.862   $15.86   $15.85   $15.90  
  Purchase #4 $94.75   8.637%   $102.9336   $102.93   $102.95   $102.90  
  Purchase #5 $250.30   9.171%   $273.255   $273.26   $273.25   $273.30  
  Purchase #6 $45.83   3.191%   $47.2924   $47.29   $47.30   $47.30  
  Purchase #7 $30.45   13.508%   $34.5632   $34.56   $34.55   $34.60  
  7 purchase totals = $554.19       $602.6067   $602.60   $602.60   $602.70