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 $104.45   13.676%   $118.7346   $118.73   $118.75   $118.70  
  Purchase #2 $59.32   6.632%   $63.2541   $63.25   $63.25   $63.30  
  Purchase #3 $140.56   11.620%   $156.8931   $156.89   $156.90   $156.90  
  Purchase #4 $186.59   12.789%   $210.453   $210.45   $210.45   $210.50  
  Purchase #5 $238.25   4.169%   $248.1826   $248.18   $248.20   $248.20  
  Purchase #6 $248.88   7.279%   $266.996   $267.00   $267.00   $267.00  
  Purchase #7 $156.26   6.128%   $165.8356   $165.84   $165.85   $165.80  
  7 purchase totals = $1,134.31       $1,230.3490   $1,230.34   $1,230.40   $1,230.40