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 $74.98   10.239%   $82.6572   $82.66   $82.65   $82.70  
  Purchase #2 $248.25   5.180%   $261.1094   $261.11   $261.10   $261.10  
  Purchase #3 $55.32   4.661%   $57.8985   $57.90   $57.90   $57.90  
  Purchase #4 $229.53   10.131%   $252.7837   $252.78   $252.80   $252.80  
  Purchase #5 $58.89   7.484%   $63.2973   $63.30   $63.30   $63.30  
  Purchase #6 $157.75   7.732%   $169.9472   $169.95   $169.95   $169.90  
  Purchase #7 $163.78   13.580%   $186.0213   $186.02   $186.00   $186.00  
  7 purchase totals = $988.50       $1,073.7146   $1,073.72   $1,073.70   $1,073.70