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 $206.62   13.511%   $234.5364   $234.54   $234.55   $234.50  
  Purchase #2 $217.82   3.796%   $226.0884   $226.09   $226.10   $226.10  
  Purchase #3 $56.35   4.179%   $58.7049   $58.70   $58.70   $58.70  
  Purchase #4 $128.73   10.638%   $142.4243   $142.42   $142.40   $142.40  
  Purchase #5 $112.59   13.346%   $127.6163   $127.62   $127.60   $127.60  
  Purchase #6 $204.66   11.112%   $227.4018   $227.40   $227.40   $227.40  
  Purchase #7 $51.95   13.428%   $58.9258   $58.93   $58.95   $58.90  
  7 purchase totals = $978.72       $1,075.6979   $1,075.70   $1,075.70   $1,075.60