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 $229.49   8.589%   $249.2009   $249.20   $249.20   $249.20  
  Purchase #2 $82.42   7.252%   $88.3971   $88.40   $88.40   $88.40  
  Purchase #3 $118.37   13.401%   $134.2328   $134.23   $134.25   $134.20  
  Purchase #4 $172.46   8.334%   $186.8328   $186.83   $186.85   $186.80  
  Purchase #5 $12.56   13.587%   $14.2665   $14.27   $14.25   $14.30  
  Purchase #6 $84.55   10.531%   $93.454   $93.45   $93.45   $93.50  
  Purchase #7 $209.73   11.509%   $233.8678   $233.87   $233.85   $233.90  
  7 purchase totals = $909.58       $1,000.2519   $1,000.25   $1,000.25   $1,000.30