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 $69.28   13.444%   $78.594   $78.59   $78.60   $78.60  
  Purchase #2 $182.84   4.254%   $190.618   $190.62   $190.60   $190.60  
  Purchase #3 $226.97   4.140%   $236.3666   $236.37   $236.35   $236.40  
  Purchase #4 $249.62   4.689%   $261.3247   $261.32   $261.30   $261.30  
  Purchase #5 $77.90   13.671%   $88.5497   $88.55   $88.55   $88.50  
  Purchase #6 $41.72   5.672%   $44.0864   $44.09   $44.10   $44.10  
  Purchase #7 $21.63   11.703%   $24.1614   $24.16   $24.15   $24.20  
  7 purchase totals = $869.96       $923.7008   $923.70   $923.65   $923.70