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 $108.80   13.655%   $123.6566   $123.66   $123.65   $123.70  
  Purchase #2 $188.63   10.111%   $207.7024   $207.70   $207.70   $207.70  
  Purchase #3 $132.41   9.849%   $145.4511   $145.45   $145.45   $145.50  
  Purchase #4 $177.62   7.691%   $191.2808   $191.28   $191.30   $191.30  
  Purchase #5 $203.35   10.487%   $224.6753   $224.68   $224.70   $224.70  
  Purchase #6 $10.75   8.145%   $11.6256   $11.63   $11.65   $11.60  
  Purchase #7 $50.89   12.306%   $57.1525   $57.15   $57.15   $57.20  
  7 purchase totals = $872.45       $961.5443   $961.55   $961.60   $961.70