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 $236.32   10.694%   $261.5921   $261.59   $261.60   $261.60  
  Purchase #2 $55.77   5.213%   $58.6773   $58.68   $58.70   $58.70  
  Purchase #3 $46.43   7.655%   $49.9842   $49.98   $50.00   $50.00  
  Purchase #4 $72.73   11.465%   $81.0685   $81.07   $81.05   $81.10  
  Purchase #5 $199.77   11.252%   $222.2481   $222.25   $222.25   $222.20  
  Purchase #6 $204.78   9.138%   $223.4928   $223.49   $223.50   $223.50  
  Purchase #7 $26.70   5.819%   $28.2537   $28.25   $28.25   $28.30  
  7 purchase totals = $842.50       $925.3167   $925.31   $925.35   $925.40