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 $56.47   11.815%   $63.1419   $63.14   $63.15   $63.10  
  Purchase #2 $235.89   5.226%   $248.2176   $248.22   $248.20   $248.20  
  Purchase #3 $119.79   9.301%   $130.9317   $130.93   $130.95   $130.90  
  Purchase #4 $126.82   11.838%   $141.833   $141.83   $141.85   $141.80  
  Purchase #5 $20.60   10.851%   $22.8353   $22.84   $22.85   $22.80  
  Purchase #6 $44.82   4.486%   $46.8306   $46.83   $46.85   $46.80  
  Purchase #7 $46.68   13.392%   $52.9314   $52.93   $52.95   $52.90  
  7 purchase totals = $651.07       $706.7215   $706.72   $706.80   $706.50