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 $109.94   3.291%   $113.5581   $113.56   $113.55   $113.60  
  Purchase #2 $195.42   4.404%   $204.0263   $204.03   $204.05   $204.00  
  Purchase #3 $98.31   3.231%   $101.4864   $101.49   $101.50   $101.50  
  Purchase #4 $38.86   3.615%   $40.2648   $40.26   $40.25   $40.30  
  Purchase #5 $232.44   10.783%   $257.504   $257.50   $257.50   $257.50  
  Purchase #6 $116.70   8.246%   $126.3231   $126.32   $126.30   $126.30  
  Purchase #7 $23.78   7.788%   $25.632   $25.63   $25.65   $25.60  
  7 purchase totals = $815.45       $868.7947   $868.79   $868.80   $868.80