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 $231.93   13.854%   $264.0616   $264.06   $264.05   $264.10  
  Purchase #2 $213.64   6.322%   $227.1463   $227.15   $227.15   $227.10  
  Purchase #3 $89.58   9.610%   $98.1886   $98.19   $98.20   $98.20  
  Purchase #4 $217.69   5.863%   $230.4532   $230.45   $230.45   $230.50  
  Purchase #5 $123.95   8.825%   $134.8886   $134.89   $134.90   $134.90  
  Purchase #6 $84.50   11.137%   $93.9108   $93.91   $93.90   $93.90  
  Purchase #7 $24.45   5.808%   $25.8701   $25.87   $25.85   $25.90  
  7 purchase totals = $985.74       $1,074.5192   $1,074.52   $1,074.50   $1,074.60