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 $208.95   11.361%   $232.6888   $232.69   $232.70   $232.70  
  Purchase #2 $26.51   9.198%   $28.9484   $28.95   $28.95   $28.90  
  Purchase #3 $122.74   11.259%   $136.5593   $136.56   $136.55   $136.60  
  Purchase #4 $53.80   7.783%   $57.9873   $57.99   $58.00   $58.00  
  Purchase #5 $96.32   12.422%   $108.2849   $108.28   $108.30   $108.30  
  Purchase #6 $215.75   12.456%   $242.6238   $242.62   $242.60   $242.60  
  Purchase #7 $238.85   8.372%   $258.8465   $258.85   $258.85   $258.80  
  7 purchase totals = $962.92       $1,065.9390   $1,065.94   $1,065.95   $1,065.90