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 $241.71   8.265%   $261.6873   $261.69   $261.70   $261.70  
  Purchase #2 $83.31   11.655%   $93.0198   $93.02   $93.00   $93.00  
  Purchase #3 $243.67   7.743%   $262.5374   $262.54   $262.55   $262.50  
  Purchase #4 $29.72   8.527%   $32.2542   $32.25   $32.25   $32.30  
  Purchase #5 $60.89   12.129%   $68.2753   $68.28   $68.30   $68.30  
  Purchase #6 $34.98   7.213%   $37.5031   $37.50   $37.50   $37.50  
  Purchase #7 $160.61   13.785%   $182.7501   $182.75   $182.75   $182.80  
  7 purchase totals = $854.89       $938.0272   $938.03   $938.05   $938.10