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 $67.58   12.695%   $76.1593   $76.16   $76.15   $76.20  
  Purchase #2 $62.54   7.154%   $67.0141   $67.01   $67.00   $67.00  
  Purchase #3 $133.41   5.458%   $140.6915   $140.69   $140.70   $140.70  
  Purchase #4 $59.44   6.389%   $63.2376   $63.24   $63.25   $63.20  
  Purchase #5 $153.80   5.164%   $161.7422   $161.74   $161.75   $161.70  
  Purchase #6 $98.74   5.728%   $104.3958   $104.40   $104.40   $104.40  
  Purchase #7 $98.78   6.465%   $105.1661   $105.17   $105.15   $105.20  
  7 purchase totals = $674.29       $718.4066   $718.41   $718.40   $718.40