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 $180.62   8.292%   $195.597   $195.60   $195.60   $195.60  
  Purchase #2 $248.75   3.632%   $257.7846   $257.78   $257.80   $257.80  
  Purchase #3 $181.61   8.719%   $197.4446   $197.44   $197.45   $197.40  
  Purchase #4 $149.43   8.294%   $161.8237   $161.82   $161.80   $161.80  
  Purchase #5 $150.47   11.764%   $168.1713   $168.17   $168.15   $168.20  
  Purchase #6 $170.26   13.399%   $193.0731   $193.07   $193.05   $193.10  
  Purchase #7 $57.90   5.189%   $60.9044   $60.90   $60.90   $60.90  
  7 purchase totals = $1,139.04       $1,234.7987   $1,234.78   $1,234.75   $1,234.80