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 $65.55   8.447%   $71.087   $71.09   $71.10   $71.10  
  Purchase #2 $65.86   11.615%   $73.5096   $73.51   $73.50   $73.50  
  Purchase #3 $187.60   11.273%   $208.7481   $208.75   $208.75   $208.70  
  Purchase #4 $218.88   12.431%   $246.089   $246.09   $246.10   $246.10  
  Purchase #5 $181.66   11.571%   $202.6799   $202.68   $202.70   $202.70  
  Purchase #6 $77.29   4.579%   $80.8291   $80.83   $80.85   $80.80  
  Purchase #7 $200.53   7.611%   $215.7923   $215.79   $215.80   $215.80  
  7 purchase totals = $997.37       $1,098.7350   $1,098.74   $1,098.80   $1,098.70