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 $58.91   7.198%   $63.1503   $63.15   $63.15   $63.20  
  Purchase #2 $104.36   10.683%   $115.5088   $115.51   $115.50   $115.50  
  Purchase #3 $202.60   12.594%   $228.1154   $228.12   $228.10   $228.10  
  Purchase #4 $73.25   6.803%   $78.2332   $78.23   $78.25   $78.20  
  Purchase #5 $163.84   12.265%   $183.935   $183.94   $183.95   $183.90  
  Purchase #6 $239.40   9.637%   $262.471   $262.47   $262.45   $262.50  
  Purchase #7 $134.92   7.150%   $144.5668   $144.57   $144.55   $144.60  
  7 purchase totals = $977.28       $1,075.9805   $1,075.99   $1,075.95   $1,076.00