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 $24.39   5.487%   $25.7283   $25.73   $25.75   $25.70  
  Purchase #2 $86.69   10.792%   $96.0456   $96.05   $96.05   $96.00  
  Purchase #3 $162.96   7.813%   $175.6921   $175.69   $175.70   $175.70  
  Purchase #4 $233.40   7.282%   $250.3962   $250.40   $250.40   $250.40  
  Purchase #5 $128.72   11.138%   $143.0568   $143.06   $143.05   $143.10  
  Purchase #6 $129.90   9.103%   $141.7248   $141.72   $141.70   $141.70  
  Purchase #7 $129.35   8.119%   $139.8519   $139.85   $139.85   $139.90  
  7 purchase totals = $895.41       $972.4957   $972.50   $972.50   $972.50