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 $217.26   6.652%   $231.7121   $231.71   $231.70   $231.70  
  Purchase #2 $54.77   3.556%   $56.7176   $56.72   $56.70   $56.70  
  Purchase #3 $107.85   6.283%   $114.6262   $114.63   $114.65   $114.60  
  Purchase #4 $22.37   6.461%   $23.8153   $23.82   $23.80   $23.80  
  Purchase #5 $132.78   3.135%   $136.9427   $136.94   $136.95   $136.90  
  Purchase #6 $44.82   6.421%   $47.6979   $47.70   $47.70   $47.70  
  Purchase #7 $241.36   9.481%   $264.2433   $264.24   $264.25   $264.20  
  7 purchase totals = $821.21       $875.7551   $875.76   $875.75   $875.60