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 $72.28   3.248%   $74.6277   $74.63   $74.65   $74.60  
  Purchase #2 $96.78   6.825%   $103.3852   $103.39   $103.40   $103.40  
  Purchase #3 $236.42   6.821%   $252.5462   $252.55   $252.55   $252.50  
  Purchase #4 $92.79   10.555%   $102.584   $102.58   $102.60   $102.60  
  Purchase #5 $5.26   8.555%   $5.71   $5.71   $5.70   $5.70  
  Purchase #6 $131.70   5.318%   $138.7038   $138.70   $138.70   $138.70  
  Purchase #7 $55.87   12.335%   $62.7616   $62.76   $62.75   $62.80  
  7 purchase totals = $691.10       $740.3185   $740.32   $740.35   $740.30