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 $242.83   7.659%   $261.4283   $261.43   $261.45   $261.40  
  Purchase #2 $10.62   11.703%   $11.8629   $11.86   $11.85   $11.90  
  Purchase #3 $82.65   11.259%   $91.9556   $91.96   $91.95   $92.00  
  Purchase #4 $218.26   5.350%   $229.9369   $229.94   $229.95   $229.90  
  Purchase #5 $208.60   8.242%   $225.7928   $225.79   $225.80   $225.80  
  Purchase #6 $38.97   5.712%   $41.196   $41.20   $41.20   $41.20  
  Purchase #7 $142.36   11.684%   $158.9933   $158.99   $159.00   $159.00  
  7 purchase totals = $944.29       $1,021.1658   $1,021.17   $1,021.20   $1,021.20