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 $222.75   4.584%   $232.9609   $232.96   $232.95   $233.00  
  Purchase #2 $185.39   12.733%   $208.9957   $209.00   $209.00   $209.00  
  Purchase #3 $239.81   12.658%   $270.1651   $270.17   $270.15   $270.20  
  Purchase #4 $44.88   3.284%   $46.3539   $46.35   $46.35   $46.40  
  Purchase #5 $117.32   6.127%   $124.5082   $124.51   $124.50   $124.50  
  Purchase #6 $94.29   13.579%   $107.0936   $107.09   $107.10   $107.10  
  Purchase #7 $201.76   13.675%   $229.3507   $229.35   $229.35   $229.40  
  7 purchase totals = $1,106.20       $1,219.4281   $1,219.43   $1,219.40   $1,219.60