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 $248.87   5.682%   $263.0108   $263.01   $263.00   $263.00  
  Purchase #2 $114.68   10.529%   $126.7547   $126.75   $126.75   $126.80  
  Purchase #3 $51.78   11.655%   $57.815   $57.82   $57.80   $57.80  
  Purchase #4 $100.94   11.147%   $112.1918   $112.19   $112.20   $112.20  
  Purchase #5 $57.25   10.206%   $63.0929   $63.09   $63.10   $63.10  
  Purchase #6 $112.42   3.223%   $116.0433   $116.04   $116.05   $116.00  
  Purchase #7 $20.46   3.652%   $21.2072   $21.21   $21.20   $21.20  
  7 purchase totals = $706.40       $760.1157   $760.11   $760.10   $760.10