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 $10.86   6.723%   $11.5901   $11.59   $11.60   $11.60  
  Purchase #2 $248.82   3.114%   $256.5683   $256.57   $256.55   $256.60  
  Purchase #3 $152.45   4.257%   $158.9398   $158.94   $158.95   $158.90  
  Purchase #4 $60.65   7.239%   $65.0405   $65.04   $65.05   $65.00  
  Purchase #5 $185.40   8.648%   $201.4334   $201.43   $201.45   $201.40  
  Purchase #6 $151.78   11.638%   $169.4442   $169.44   $169.45   $169.40  
  Purchase #7 $249.80   9.354%   $273.1663   $273.17   $273.15   $273.20  
  7 purchase totals = $1,059.76       $1,136.1826   $1,136.18   $1,136.20   $1,136.10