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 $78.61   8.752%   $85.4899   $85.49   $85.50   $85.50  
  Purchase #2 $109.25   7.403%   $117.3378   $117.34   $117.35   $117.30  
  Purchase #3 $236.69   12.120%   $265.3768   $265.38   $265.40   $265.40  
  Purchase #4 $245.98   3.538%   $254.6828   $254.68   $254.70   $254.70  
  Purchase #5 $107.91   7.396%   $115.891   $115.89   $115.90   $115.90  
  Purchase #6 $153.46   7.528%   $165.0125   $165.01   $165.00   $165.00  
  Purchase #7 $202.43   6.610%   $215.8106   $215.81   $215.80   $215.80  
  7 purchase totals = $1,134.33       $1,219.6014   $1,219.60   $1,219.65   $1,219.60