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 $153.78   8.113%   $166.2562   $166.26   $166.25   $166.30  
  Purchase #2 $56.31   13.487%   $63.9045   $63.90   $63.90   $63.90  
  Purchase #3 $246.32   6.483%   $262.2889   $262.29   $262.30   $262.30  
  Purchase #4 $51.95   9.202%   $56.7304   $56.73   $56.75   $56.70  
  Purchase #5 $164.32   11.694%   $183.5356   $183.54   $183.55   $183.50  
  Purchase #6 $15.76   11.623%   $17.5918   $17.59   $17.60   $17.60  
  Purchase #7 $169.77   12.792%   $191.487   $191.49   $191.50   $191.50  
  7 purchase totals = $858.21       $941.7944   $941.80   $941.85   $941.80