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 $62.58   8.536%   $67.9218   $67.92   $67.90   $67.90  
  Purchase #2 $14.79   5.237%   $15.5646   $15.56   $15.55   $15.60  
  Purchase #3 $80.61   5.682%   $85.1903   $85.19   $85.20   $85.20  
  Purchase #4 $136.58   10.631%   $151.0998   $151.10   $151.10   $151.10  
  Purchase #5 $163.83   10.210%   $180.557   $180.56   $180.55   $180.60  
  Purchase #6 $142.33   6.252%   $151.2285   $151.23   $151.25   $151.20  
  Purchase #7 $72.31   3.386%   $74.7584   $74.76   $74.75   $74.80  
  7 purchase totals = $673.03       $726.3204   $726.32   $726.30   $726.40