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 $117.61   13.232%   $133.1722   $133.17   $133.15   $133.20  
  Purchase #2 $17.31   8.554%   $18.7907   $18.79   $18.80   $18.80  
  Purchase #3 $185.76   4.234%   $193.6251   $193.63   $193.65   $193.60  
  Purchase #4 $185.74   12.656%   $209.2473   $209.25   $209.25   $209.20  
  Purchase #5 $213.38   8.207%   $230.8921   $230.89   $230.90   $230.90  
  Purchase #6 $90.80   11.137%   $100.9124   $100.91   $100.90   $100.90  
  Purchase #7 $34.97   8.347%   $37.8889   $37.89   $37.90   $37.90  
  7 purchase totals = $845.57       $924.5287   $924.53   $924.55   $924.50