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 $192.48   4.549%   $201.2359   $201.24   $201.25   $201.20  
  Purchase #2 $61.70   6.335%   $65.6087   $65.61   $65.60   $65.60  
  Purchase #3 $210.35   12.180%   $235.9706   $235.97   $235.95   $236.00  
  Purchase #4 $10.57   12.677%   $11.91   $11.91   $11.90   $11.90  
  Purchase #5 $200.51   7.476%   $215.5001   $215.50   $215.50   $215.50  
  Purchase #6 $142.79   6.712%   $152.3741   $152.37   $152.35   $152.40  
  Purchase #7 $130.77   4.827%   $137.0823   $137.08   $137.10   $137.10  
  7 purchase totals = $949.17       $1,019.6817   $1,019.68   $1,019.65   $1,019.70