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 $211.58   4.822%   $221.7824   $221.78   $221.80   $221.80  
  Purchase #2 $92.51   3.840%   $96.0624   $96.06   $96.05   $96.10  
  Purchase #3 $76.80   6.283%   $81.6253   $81.63   $81.65   $81.60  
  Purchase #4 $46.71   12.386%   $52.4955   $52.50   $52.50   $52.50  
  Purchase #5 $227.89   11.158%   $253.318   $253.32   $253.30   $253.30  
  Purchase #6 $214.90   11.597%   $239.822   $239.82   $239.80   $239.80  
  Purchase #7 $91.43   7.627%   $98.4034   $98.40   $98.40   $98.40  
  7 purchase totals = $961.82       $1,043.5090   $1,043.51   $1,043.50   $1,043.50