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 $53.61   5.172%   $56.3827   $56.38   $56.40   $56.40  
  Purchase #2 $148.92   8.548%   $161.6497   $161.65   $161.65   $161.60  
  Purchase #3 $132.58   10.700%   $146.7661   $146.77   $146.75   $146.80  
  Purchase #4 $226.37   10.542%   $250.2339   $250.23   $250.25   $250.20  
  Purchase #5 $33.92   8.844%   $36.9199   $36.92   $36.90   $36.90  
  Purchase #6 $161.71   12.577%   $182.0483   $182.05   $182.05   $182.00  
  Purchase #7 $196.44   6.155%   $208.5309   $208.53   $208.55   $208.50  
  7 purchase totals = $953.55       $1,042.5315   $1,042.53   $1,042.55   $1,042.40