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 $111.76   11.845%   $124.998   $125.00   $125.00   $125.00  
  Purchase #2 $87.55   7.182%   $93.8378   $93.84   $93.85   $93.80  
  Purchase #3 $179.89   5.423%   $189.6454   $189.65   $189.65   $189.60  
  Purchase #4 $104.29   10.233%   $114.962   $114.96   $114.95   $115.00  
  Purchase #5 $105.53   13.309%   $119.575   $119.58   $119.60   $119.60  
  Purchase #6 $133.89   10.293%   $147.6713   $147.67   $147.65   $147.70  
  Purchase #7 $67.34   7.770%   $72.5723   $72.57   $72.55   $72.60  
  7 purchase totals = $790.25       $863.2618   $863.27   $863.25   $863.30