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 $25.71   3.695%   $26.66   $26.66   $26.65   $26.70  
  Purchase #2 $48.97   10.771%   $54.2446   $54.24   $54.25   $54.20  
  Purchase #3 $72.90   7.755%   $78.5534   $78.55   $78.55   $78.60  
  Purchase #4 $48.42   8.735%   $52.6495   $52.65   $52.65   $52.60  
  Purchase #5 $16.26   8.422%   $17.6294   $17.63   $17.65   $17.60  
  Purchase #6 $68.44   6.159%   $72.6552   $72.66   $72.65   $72.70  
  Purchase #7 $227.42   6.774%   $242.8254   $242.83   $242.85   $242.80  
  7 purchase totals = $508.12       $545.2175   $545.22   $545.25   $545.20