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 $233.64   12.629%   $263.1464   $263.15   $263.15   $263.10  
  Purchase #2 $154.91   7.351%   $166.2974   $166.30   $166.30   $166.30  
  Purchase #3 $22.48   5.554%   $23.7285   $23.73   $23.75   $23.70  
  Purchase #4 $174.66   4.659%   $182.7974   $182.80   $182.80   $182.80  
  Purchase #5 $99.48   6.165%   $105.6129   $105.61   $105.60   $105.60  
  Purchase #6 $185.88   5.862%   $196.7763   $196.78   $196.80   $196.80  
  Purchase #7 $163.97   11.591%   $182.9758   $182.98   $183.00   $183.00  
  7 purchase totals = $1,035.02       $1,121.3347   $1,121.35   $1,121.40   $1,121.30