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 $229.41   5.569%   $242.1858   $242.19   $242.20   $242.20  
  Purchase #2 $110.62   6.177%   $117.453   $117.45   $117.45   $117.50  
  Purchase #3 $186.58   6.289%   $198.314   $198.31   $198.30   $198.30  
  Purchase #4 $232.97   8.351%   $252.4253   $252.43   $252.45   $252.40  
  Purchase #5 $237.68   9.260%   $259.6892   $259.69   $259.70   $259.70  
  Purchase #6 $97.49   6.510%   $103.8366   $103.84   $103.85   $103.80  
  Purchase #7 $67.59   6.516%   $71.9942   $71.99   $72.00   $72.00  
  7 purchase totals = $1,162.34       $1,245.8981   $1,245.90   $1,245.95   $1,245.90