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 $218.56   13.481%   $248.0241   $248.02   $248.00   $248.00  
  Purchase #2 $187.51   7.299%   $201.1964   $201.20   $201.20   $201.20  
  Purchase #3 $105.61   11.751%   $118.0202   $118.02   $118.00   $118.00  
  Purchase #4 $226.37   5.306%   $238.3812   $238.38   $238.40   $238.40  
  Purchase #5 $242.89   3.284%   $250.8665   $250.87   $250.85   $250.90  
  Purchase #6 $198.89   4.344%   $207.5298   $207.53   $207.55   $207.50  
  Purchase #7 $74.75   10.383%   $82.5113   $82.51   $82.50   $82.50  
  7 purchase totals = $1,254.58       $1,346.5295   $1,346.53   $1,346.50   $1,346.50