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 $218.91   7.474%   $235.2713   $235.27   $235.25   $235.30  
  Purchase #2 $89.45   6.308%   $95.0925   $95.09   $95.10   $95.10  
  Purchase #3 $212.76   8.192%   $230.1893   $230.19   $230.20   $230.20  
  Purchase #4 $199.87   13.458%   $226.7685   $226.77   $226.75   $226.80  
  Purchase #5 $226.37   10.435%   $249.9917   $249.99   $250.00   $250.00  
  Purchase #6 $188.97   9.332%   $206.6047   $206.60   $206.60   $206.60  
  Purchase #7 $46.51   12.702%   $52.4177   $52.42   $52.40   $52.40  
  7 purchase totals = $1,182.84       $1,296.3357   $1,296.33   $1,296.30   $1,296.40