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 $201.57   10.768%   $223.2751   $223.28   $223.30   $223.30  
  Purchase #2 $11.68   12.637%   $13.156   $13.16   $13.15   $13.20  
  Purchase #3 $244.80   10.655%   $270.8834   $270.88   $270.90   $270.90  
  Purchase #4 $174.29   4.783%   $182.6263   $182.63   $182.65   $182.60  
  Purchase #5 $238.64   10.150%   $262.862   $262.86   $262.85   $262.90  
  Purchase #6 $229.41   8.296%   $248.4419   $248.44   $248.45   $248.40  
  Purchase #7 $201.47   3.529%   $208.5799   $208.58   $208.60   $208.60  
  7 purchase totals = $1,301.86       $1,409.8246   $1,409.83   $1,409.90   $1,409.90