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 $166.60   8.835%   $181.3191   $181.32   $181.30   $181.30  
  Purchase #2 $176.77   12.382%   $198.6577   $198.66   $198.65   $198.70  
  Purchase #3 $25.76   6.373%   $27.4017   $27.40   $27.40   $27.40  
  Purchase #4 $206.30   3.808%   $214.1559   $214.16   $214.15   $214.20  
  Purchase #5 $66.56   13.597%   $75.6102   $75.61   $75.60   $75.60  
  Purchase #6 $195.83   7.682%   $210.8737   $210.87   $210.85   $210.90  
  Purchase #7 $154.64   3.315%   $159.7663   $159.77   $159.75   $159.80  
  7 purchase totals = $992.46       $1,067.7846   $1,067.79   $1,067.70   $1,067.90