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 $224.96   12.493%   $253.0643   $253.06   $253.05   $253.10  
  Purchase #2 $177.40   5.691%   $187.4958   $187.50   $187.50   $187.50  
  Purchase #3 $68.27   11.655%   $76.2269   $76.23   $76.25   $76.20  
  Purchase #4 $171.72   10.493%   $189.7386   $189.74   $189.75   $189.70  
  Purchase #5 $185.36   4.488%   $193.679   $193.68   $193.70   $193.70  
  Purchase #6 $132.72   5.438%   $139.9373   $139.94   $139.95   $139.90  
  Purchase #7 $44.63   4.646%   $46.7035   $46.70   $46.70   $46.70  
  7 purchase totals = $1,005.06       $1,086.8454   $1,086.85   $1,086.90   $1,086.80