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 $60.92   3.527%   $63.0686   $63.07   $63.05   $63.10  
  Purchase #2 $122.87   9.416%   $134.4394   $134.44   $134.45   $134.40  
  Purchase #3 $87.72   10.701%   $97.1069   $97.11   $97.10   $97.10  
  Purchase #4 $67.98   4.321%   $70.9174   $70.92   $70.90   $70.90  
  Purchase #5 $5.37   3.870%   $5.5778   $5.58   $5.60   $5.60  
  Purchase #6 $249.67   11.510%   $278.407   $278.41   $278.40   $278.40  
  Purchase #7 $98.54   9.316%   $107.72   $107.72   $107.70   $107.70  
  7 purchase totals = $693.07       $757.2371   $757.25   $757.20   $757.20