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 $110.34   8.474%   $119.6902   $119.69   $119.70   $119.70  
  Purchase #2 $186.38   12.776%   $210.1919   $210.19   $210.20   $210.20  
  Purchase #3 $168.97   9.865%   $185.6389   $185.64   $185.65   $185.60  
  Purchase #4 $159.62   7.478%   $171.5564   $171.56   $171.55   $171.60  
  Purchase #5 $50.82   4.338%   $53.0246   $53.02   $53.00   $53.00  
  Purchase #6 $226.34   5.842%   $239.5628   $239.56   $239.55   $239.60  
  Purchase #7 $232.28   11.490%   $258.969   $258.97   $258.95   $259.00  
  7 purchase totals = $1,134.75       $1,238.6338   $1,238.63   $1,238.60   $1,238.70