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 $200.55   12.811%   $226.2425   $226.24   $226.25   $226.20  
  Purchase #2 $137.54   7.451%   $147.7881   $147.79   $147.80   $147.80  
  Purchase #3 $61.41   3.192%   $63.3702   $63.37   $63.35   $63.40  
  Purchase #4 $164.77   11.652%   $183.969   $183.97   $183.95   $184.00  
  Purchase #5 $182.94   4.644%   $191.4357   $191.44   $191.45   $191.40  
  Purchase #6 $235.85   13.623%   $267.9798   $267.98   $268.00   $268.00  
  Purchase #7 $119.86   4.801%   $125.6145   $125.61   $125.60   $125.60  
  7 purchase totals = $1,102.92       $1,206.3998   $1,206.40   $1,206.40   $1,206.40