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 $92.79   11.579%   $103.5342   $103.53   $103.55   $103.50  
  Purchase #2 $195.63   8.680%   $212.6107   $212.61   $212.60   $212.60  
  Purchase #3 $166.28   12.267%   $186.6776   $186.68   $186.70   $186.70  
  Purchase #4 $246.51   11.719%   $275.3985   $275.40   $275.40   $275.40  
  Purchase #5 $119.70   5.480%   $126.2596   $126.26   $126.25   $126.30  
  Purchase #6 $54.43   5.818%   $57.5967   $57.60   $57.60   $57.60  
  Purchase #7 $165.69   3.448%   $171.403   $171.40   $171.40   $171.40  
  7 purchase totals = $1,041.03       $1,133.4803   $1,133.48   $1,133.50   $1,133.50