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 $172.31   7.408%   $185.0747   $185.07   $185.05   $185.10  
  Purchase #2 $230.32   12.444%   $258.981   $258.98   $259.00   $259.00  
  Purchase #3 $15.99   4.485%   $16.7072   $16.71   $16.70   $16.70  
  Purchase #4 $74.71   13.595%   $84.8668   $84.87   $84.85   $84.90  
  Purchase #5 $24.68   13.675%   $28.055   $28.06   $28.05   $28.10  
  Purchase #6 $170.54   8.860%   $185.6498   $185.65   $185.65   $185.60  
  Purchase #7 $127.68   3.275%   $131.8615   $131.86   $131.85   $131.90  
  7 purchase totals = $816.23       $891.1960   $891.20   $891.15   $891.30