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 $114.61   4.384%   $119.6345   $119.63   $119.65   $119.60  
  Purchase #2 $148.28   3.766%   $153.8642   $153.86   $153.85   $153.90  
  Purchase #3 $122.91   7.826%   $132.5289   $132.53   $132.55   $132.50  
  Purchase #4 $101.62   5.794%   $107.5079   $107.51   $107.50   $107.50  
  Purchase #5 $70.82   4.655%   $74.1167   $74.12   $74.10   $74.10  
  Purchase #6 $228.89   9.441%   $250.4995   $250.50   $250.50   $250.50  
  Purchase #7 $188.44   5.496%   $198.7967   $198.80   $198.80   $198.80  
  7 purchase totals = $975.57       $1,036.9484   $1,036.95   $1,036.95   $1,036.90