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 $55.70   8.802%   $60.6027   $60.60   $60.60   $60.60  
  Purchase #2 $218.67   12.846%   $246.7603   $246.76   $246.75   $246.80  
  Purchase #3 $81.25   5.514%   $85.7301   $85.73   $85.75   $85.70  
  Purchase #4 $151.41   10.359%   $167.0946   $167.09   $167.10   $167.10  
  Purchase #5 $215.25   4.576%   $225.0998   $225.10   $225.10   $225.10  
  Purchase #6 $127.77   6.621%   $136.2297   $136.23   $136.25   $136.20  
  Purchase #7 $76.84   10.487%   $84.8982   $84.90   $84.90   $84.90  
  7 purchase totals = $926.89       $1,006.4154   $1,006.41   $1,006.45   $1,006.40