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 $87.77   11.699%   $98.0382   $98.04   $98.05   $98.00  
  Purchase #2 $108.99   5.194%   $114.6509   $114.65   $114.65   $114.70  
  Purchase #3 $124.56   5.738%   $131.7073   $131.71   $131.70   $131.70  
  Purchase #4 $40.51   9.682%   $44.4322   $44.43   $44.45   $44.40  
  Purchase #5 $8.80   13.786%   $10.0132   $10.01   $10.00   $10.00  
  Purchase #6 $212.98   10.438%   $235.2109   $235.21   $235.20   $235.20  
  Purchase #7 $138.71   12.505%   $156.0557   $156.06   $156.05   $156.10  
  7 purchase totals = $722.32       $790.1084   $790.11   $790.10   $790.10