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 $212.58   12.505%   $239.1631   $239.16   $239.15   $239.20  
  Purchase #2 $43.42   7.765%   $46.7916   $46.79   $46.80   $46.80  
  Purchase #3 $140.88   4.195%   $146.7899   $146.79   $146.80   $146.80  
  Purchase #4 $213.58   13.562%   $242.5457   $242.55   $242.55   $242.50  
  Purchase #5 $48.54   8.246%   $52.5426   $52.54   $52.55   $52.50  
  Purchase #6 $77.83   6.542%   $82.9216   $82.92   $82.90   $82.90  
  Purchase #7 $102.46   11.565%   $114.3095   $114.31   $114.30   $114.30  
  7 purchase totals = $839.29       $925.0640   $925.06   $925.05   $925.00