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 $212.88   12.623%   $239.7518   $239.75   $239.75   $239.80  
  Purchase #2 $118.72   3.869%   $123.3133   $123.31   $123.30   $123.30  
  Purchase #3 $19.73   12.218%   $22.1406   $22.14   $22.15   $22.10  
  Purchase #4 $109.60   7.688%   $118.026   $118.03   $118.05   $118.00  
  Purchase #5 $104.55   10.150%   $115.1618   $115.16   $115.15   $115.20  
  Purchase #6 $82.38   6.565%   $87.7882   $87.79   $87.80   $87.80  
  Purchase #7 $59.58   6.684%   $63.5623   $63.56   $63.55   $63.60  
  7 purchase totals = $707.44       $769.7440   $769.74   $769.75   $769.80