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 $49.87   6.503%   $53.113   $53.11   $53.10   $53.10  
  Purchase #2 $151.44   5.719%   $160.1009   $160.10   $160.10   $160.10  
  Purchase #3 $69.81   11.465%   $77.8137   $77.81   $77.80   $77.80  
  Purchase #4 $205.78   5.604%   $217.3119   $217.31   $217.30   $217.30  
  Purchase #5 $223.78   11.289%   $249.0425   $249.04   $249.05   $249.00  
  Purchase #6 $171.99   10.863%   $190.6733   $190.67   $190.65   $190.70  
  Purchase #7 $75.64   12.677%   $85.2289   $85.23   $85.25   $85.20  
  7 purchase totals = $948.31       $1,033.2842   $1,033.27   $1,033.25   $1,033.20