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 $81.97   5.696%   $86.639   $86.64   $86.65   $86.60  
  Purchase #2 $13.38   10.236%   $14.7496   $14.75   $14.75   $14.70  
  Purchase #3 $68.36   9.287%   $74.7086   $74.71   $74.70   $74.70  
  Purchase #4 $58.74   10.276%   $64.7761   $64.78   $64.80   $64.80  
  Purchase #5 $22.81   9.304%   $24.9322   $24.93   $24.95   $24.90  
  Purchase #6 $52.96   7.355%   $56.8552   $56.86   $56.85   $56.90  
  Purchase #7 $78.42   3.343%   $81.0416   $81.04   $81.05   $81.00  
  7 purchase totals = $376.64       $403.7023   $403.71   $403.75   $403.60