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 $60.93   7.642%   $65.5863   $65.59   $65.60   $65.60  
  Purchase #2 $34.32   3.624%   $35.5638   $35.56   $35.55   $35.60  
  Purchase #3 $44.26   12.167%   $49.6451   $49.65   $49.65   $49.60  
  Purchase #4 $178.81   12.864%   $201.8121   $201.81   $201.80   $201.80  
  Purchase #5 $132.63   6.290%   $140.9724   $140.97   $140.95   $141.00  
  Purchase #6 $181.51   9.126%   $198.0746   $198.07   $198.05   $198.10  
  Purchase #7 $11.87   10.231%   $13.0844   $13.08   $13.10   $13.10  
  7 purchase totals = $644.33       $704.7387   $704.73   $704.70   $704.80