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 $221.49   8.137%   $239.5126   $239.51   $239.50   $239.50  
  Purchase #2 $37.59   10.772%   $41.6392   $41.64   $41.65   $41.60  
  Purchase #3 $19.27   10.205%   $21.2365   $21.24   $21.25   $21.20  
  Purchase #4 $167.58   3.518%   $173.4755   $173.48   $173.50   $173.50  
  Purchase #5 $8.71   7.861%   $9.3947   $9.39   $9.40   $9.40  
  Purchase #6 $182.91   8.139%   $197.797   $197.80   $197.80   $197.80  
  Purchase #7 $83.72   5.708%   $88.4987   $88.50   $88.50   $88.50  
  7 purchase totals = $721.27       $771.5542   $771.56   $771.60   $771.50