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 $166.68   11.744%   $186.2549   $186.25   $186.25   $186.30  
  Purchase #2 $104.77   8.390%   $113.5602   $113.56   $113.55   $113.60  
  Purchase #3 $44.47   4.143%   $46.3124   $46.31   $46.30   $46.30  
  Purchase #4 $211.65   10.147%   $233.1261   $233.13   $233.15   $233.10  
  Purchase #5 $185.55   4.313%   $193.5528   $193.55   $193.55   $193.60  
  Purchase #6 $174.37   9.365%   $190.6998   $190.70   $190.70   $190.70  
  Purchase #7 $238.74   6.168%   $253.4655   $253.47   $253.45   $253.50  
  7 purchase totals = $1,126.23       $1,216.9717   $1,216.97   $1,216.95   $1,217.10