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 $232.98   5.869%   $246.6536   $246.65   $246.65   $246.70  
  Purchase #2 $246.34   9.401%   $269.4984   $269.50   $269.50   $269.50  
  Purchase #3 $205.91   12.411%   $231.4655   $231.47   $231.45   $231.50  
  Purchase #4 $126.48   8.389%   $137.0904   $137.09   $137.10   $137.10  
  Purchase #5 $93.80   9.596%   $102.801   $102.80   $102.80   $102.80  
  Purchase #6 $144.67   6.451%   $154.0027   $154.00   $154.00   $154.00  
  Purchase #7 $108.48   8.646%   $117.8592   $117.86   $117.85   $117.90  
  7 purchase totals = $1,158.66       $1,259.3708   $1,259.37   $1,259.35   $1,259.50