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 $127.47   11.174%   $141.7135   $141.71   $141.70   $141.70  
  Purchase #2 $24.38   5.308%   $25.6741   $25.67   $25.65   $25.70  
  Purchase #3 $235.31   13.236%   $266.4556   $266.46   $266.45   $266.50  
  Purchase #4 $94.44   13.435%   $107.128   $107.13   $107.15   $107.10  
  Purchase #5 $7.96   6.478%   $8.4756   $8.48   $8.50   $8.50  
  Purchase #6 $208.99   4.249%   $217.87   $217.87   $217.85   $217.90  
  Purchase #7 $10.87   8.790%   $11.8255   $11.83   $11.85   $11.80  
  7 purchase totals = $709.42       $779.1423   $779.15   $779.15   $779.20