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 $247.26   6.116%   $262.3824   $262.38   $262.40   $262.40  
  Purchase #2 $205.58   9.434%   $224.9744   $224.97   $224.95   $225.00  
  Purchase #3 $233.72   9.561%   $256.066   $256.07   $256.05   $256.10  
  Purchase #4 $113.68   12.482%   $127.8695   $127.87   $127.85   $127.90  
  Purchase #5 $111.41   8.755%   $121.1639   $121.16   $121.15   $121.20  
  Purchase #6 $6.26   6.790%   $6.6851   $6.69   $6.70   $6.70  
  Purchase #7 $7.93   10.767%   $8.7838   $8.78   $8.80   $8.80  
  7 purchase totals = $925.84       $1,007.9251   $1,007.92   $1,007.90   $1,008.10