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 $103.84   10.654%   $114.9031   $114.90   $114.90   $114.90  
  Purchase #2 $55.33   4.196%   $57.6516   $57.65   $57.65   $57.70  
  Purchase #3 $156.40   7.852%   $168.6805   $168.68   $168.70   $168.70  
  Purchase #4 $10.77   9.267%   $11.7681   $11.77   $11.75   $11.80  
  Purchase #5 $199.66   7.729%   $215.0917   $215.09   $215.10   $215.10  
  Purchase #6 $216.41   11.291%   $240.8449   $240.84   $240.85   $240.80  
  Purchase #7 $196.93   9.490%   $215.6187   $215.62   $215.60   $215.60  
  7 purchase totals = $939.34       $1,024.5586   $1,024.55   $1,024.55   $1,024.60