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 $13.47   5.676%   $14.2346   $14.23   $14.25   $14.20  
  Purchase #2 $54.77   3.283%   $56.5681   $56.57   $56.55   $56.60  
  Purchase #3 $176.44   13.873%   $200.9175   $200.92   $200.90   $200.90  
  Purchase #4 $246.67   5.676%   $260.671   $260.67   $260.65   $260.70  
  Purchase #5 $227.86   5.293%   $239.9206   $239.92   $239.90   $239.90  
  Purchase #6 $229.92   9.675%   $252.1648   $252.16   $252.15   $252.20  
  Purchase #7 $161.67   7.362%   $173.5721   $173.57   $173.55   $173.60  
  7 purchase totals = $1,110.80       $1,198.0487   $1,198.04   $1,197.95   $1,198.10