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 $196.45   6.472%   $209.1642   $209.16   $209.15   $209.20  
  Purchase #2 $175.27   11.243%   $194.9756   $194.98   $195.00   $195.00  
  Purchase #3 $187.61   12.581%   $211.2132   $211.21   $211.20   $211.20  
  Purchase #4 $88.32   8.493%   $95.821   $95.82   $95.80   $95.80  
  Purchase #5 $72.78   13.290%   $82.4525   $82.45   $82.45   $82.50  
  Purchase #6 $12.97   7.566%   $13.9513   $13.95   $13.95   $14.00  
  Purchase #7 $250.85   4.278%   $261.5814   $261.58   $261.60   $261.60  
  7 purchase totals = $984.25       $1,069.1592   $1,069.15   $1,069.15   $1,069.30