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 $51.54   3.507%   $53.3475   $53.35   $53.35   $53.30  
  Purchase #2 $93.81   12.151%   $105.2089   $105.21   $105.20   $105.20  
  Purchase #3 $146.64   6.356%   $155.9604   $155.96   $155.95   $156.00  
  Purchase #4 $236.96   10.461%   $261.7484   $261.75   $261.75   $261.70  
  Purchase #5 $149.81   13.785%   $170.4613   $170.46   $170.45   $170.50  
  Purchase #6 $89.98   10.631%   $99.5458   $99.55   $99.55   $99.50  
  Purchase #7 $118.37   5.411%   $124.775   $124.78   $124.80   $124.80  
  7 purchase totals = $887.11       $971.0473   $971.06   $971.05   $971.00