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 $107.33   7.111%   $114.9622   $114.96   $114.95   $115.00  
  Purchase #2 $156.53   13.618%   $177.8463   $177.85   $177.85   $177.80  
  Purchase #3 $80.91   3.866%   $84.038   $84.04   $84.05   $84.00  
  Purchase #4 $187.45   8.192%   $202.8059   $202.81   $202.80   $202.80  
  Purchase #5 $47.39   4.648%   $49.5927   $49.59   $49.60   $49.60  
  Purchase #6 $72.39   6.800%   $77.3125   $77.31   $77.30   $77.30  
  Purchase #7 $241.48   5.154%   $253.9259   $253.93   $253.95   $253.90  
  7 purchase totals = $893.48       $960.4835   $960.49   $960.50   $960.40