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 $183.85   11.664%   $205.2943   $205.29   $205.30   $205.30  
  Purchase #2 $34.79   6.662%   $37.1077   $37.11   $37.10   $37.10  
  Purchase #3 $53.54   9.557%   $58.6568   $58.66   $58.65   $58.70  
  Purchase #4 $241.82   9.578%   $264.9815   $264.98   $265.00   $265.00  
  Purchase #5 $46.93   5.724%   $49.6163   $49.62   $49.60   $49.60  
  Purchase #6 $46.48   5.533%   $49.0517   $49.05   $49.05   $49.10  
  Purchase #7 $31.86   8.770%   $34.6541   $34.65   $34.65   $34.70  
  7 purchase totals = $639.27       $699.3624   $699.36   $699.35   $699.50