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 $192.57   6.568%   $205.218   $205.22   $205.20   $205.20  
  Purchase #2 $80.62   8.202%   $87.2325   $87.23   $87.25   $87.20  
  Purchase #3 $249.94   8.614%   $271.4698   $271.47   $271.45   $271.50  
  Purchase #4 $248.53   4.211%   $258.9956   $259.00   $259.00   $259.00  
  Purchase #5 $185.72   4.165%   $193.4552   $193.46   $193.45   $193.50  
  Purchase #6 $30.70   11.799%   $34.3223   $34.32   $34.30   $34.30  
  Purchase #7 $85.51   12.525%   $96.2201   $96.22   $96.20   $96.20  
  7 purchase totals = $1,073.59       $1,146.9135   $1,146.92   $1,146.85   $1,146.90