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 $56.31   9.685%   $61.7636   $61.76   $61.75   $61.80  
  Purchase #2 $151.33   12.615%   $170.4203   $170.42   $170.40   $170.40  
  Purchase #3 $57.45   11.391%   $63.9941   $63.99   $64.00   $64.00  
  Purchase #4 $164.81   5.833%   $174.4234   $174.42   $174.40   $174.40  
  Purchase #5 $70.51   8.632%   $76.5964   $76.60   $76.60   $76.60  
  Purchase #6 $99.64   13.439%   $113.0306   $113.03   $113.05   $113.00  
  Purchase #7 $107.56   4.232%   $112.1119   $112.11   $112.10   $112.10  
  7 purchase totals = $707.61       $772.3403   $772.33   $772.30   $772.30