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 $196.49   4.860%   $206.0394   $206.04   $206.05   $206.00  
  Purchase #2 $224.41   12.854%   $253.2557   $253.26   $253.25   $253.30  
  Purchase #3 $128.36   4.456%   $134.0797   $134.08   $134.10   $134.10  
  Purchase #4 $229.94   5.873%   $243.4444   $243.44   $243.45   $243.40  
  Purchase #5 $52.90   6.682%   $56.4348   $56.43   $56.45   $56.40  
  Purchase #6 $232.42   3.376%   $240.2665   $240.27   $240.25   $240.30  
  Purchase #7 $226.54   3.830%   $235.2165   $235.22   $235.20   $235.20  
  7 purchase totals = $1,291.06       $1,368.7370   $1,368.74   $1,368.75   $1,368.70