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 $200.96   13.723%   $228.5377   $228.54   $228.55   $228.50  
  Purchase #2 $46.94   5.166%   $49.3649   $49.36   $49.35   $49.40  
  Purchase #3 $196.71   7.633%   $211.7249   $211.72   $211.70   $211.70  
  Purchase #4 $85.27   13.647%   $96.9068   $96.91   $96.90   $96.90  
  Purchase #5 $163.79   3.627%   $169.7307   $169.73   $169.75   $169.70  
  Purchase #6 $199.80   10.832%   $221.4423   $221.44   $221.45   $221.40  
  Purchase #7 $248.35   13.378%   $281.5743   $281.57   $281.55   $281.60  
  7 purchase totals = $1,141.82       $1,259.2816   $1,259.27   $1,259.25   $1,259.20