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 $91.55   3.332%   $94.6004   $94.60   $94.60   $94.60  
  Purchase #2 $56.49   5.694%   $59.7065   $59.71   $59.70   $59.70  
  Purchase #3 $66.57   13.141%   $75.318   $75.32   $75.30   $75.30  
  Purchase #4 $23.62   3.115%   $24.3558   $24.36   $24.35   $24.40  
  Purchase #5 $236.25   9.690%   $259.1426   $259.14   $259.15   $259.10  
  Purchase #6 $144.80   9.234%   $158.1708   $158.17   $158.15   $158.20  
  Purchase #7 $245.29   12.631%   $276.2726   $276.27   $276.25   $276.30  
  7 purchase totals = $864.57       $947.5667   $947.57   $947.50   $947.60