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 $111.81   12.325%   $125.5906   $125.59   $125.60   $125.60  
  Purchase #2 $182.51   7.192%   $195.6361   $195.64   $195.65   $195.60  
  Purchase #3 $65.77   5.272%   $69.2374   $69.24   $69.25   $69.20  
  Purchase #4 $157.59   13.243%   $178.4596   $178.46   $178.45   $178.50  
  Purchase #5 $214.46   3.403%   $221.7581   $221.76   $221.75   $221.80  
  Purchase #6 $212.58   11.775%   $237.6113   $237.61   $237.60   $237.60  
  Purchase #7 $141.68   7.635%   $152.4973   $152.50   $152.50   $152.50  
  7 purchase totals = $1,086.40       $1,180.7904   $1,180.80   $1,180.80   $1,180.80