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 $23.59   12.448%   $26.5265   $26.53   $26.55   $26.50  
  Purchase #2 $144.92   9.679%   $158.9468   $158.95   $158.95   $158.90  
  Purchase #3 $182.58   13.629%   $207.4638   $207.46   $207.45   $207.50  
  Purchase #4 $74.56   3.314%   $77.0309   $77.03   $77.05   $77.00  
  Purchase #5 $235.85   8.477%   $255.843   $255.84   $255.85   $255.80  
  Purchase #6 $7.48   9.321%   $8.1772   $8.18   $8.20   $8.20  
  Purchase #7 $149.90   13.834%   $170.6372   $170.64   $170.65   $170.60  
  7 purchase totals = $818.88       $904.6254   $904.63   $904.70   $904.50