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 $193.35   10.798%   $214.2279   $214.23   $214.25   $214.20  
  Purchase #2 $152.25   5.235%   $160.2203   $160.22   $160.20   $160.20  
  Purchase #3 $41.65   11.584%   $46.4747   $46.47   $46.45   $46.50  
  Purchase #4 $240.80   10.120%   $265.169   $265.17   $265.15   $265.20  
  Purchase #5 $49.36   3.105%   $50.8926   $50.89   $50.90   $50.90  
  Purchase #6 $235.70   5.841%   $249.4672   $249.47   $249.45   $249.50  
  Purchase #7 $125.34   11.534%   $139.7967   $139.80   $139.80   $139.80  
  7 purchase totals = $1,038.45       $1,126.2484   $1,126.25   $1,126.20   $1,126.30