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 $73.59   4.379%   $76.8125   $76.81   $76.80   $76.80  
  Purchase #2 $237.82   8.868%   $258.9099   $258.91   $258.90   $258.90  
  Purchase #3 $13.86   8.588%   $15.0503   $15.05   $15.05   $15.10  
  Purchase #4 $97.44   5.544%   $102.8421   $102.84   $102.85   $102.80  
  Purchase #5 $240.28   6.366%   $255.5762   $255.58   $255.60   $255.60  
  Purchase #6 $223.70   10.147%   $246.3988   $246.40   $246.40   $246.40  
  Purchase #7 $108.33   7.463%   $116.4147   $116.41   $116.40   $116.40  
  7 purchase totals = $995.02       $1,072.0045   $1,072.00   $1,072.00   $1,072.00