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 $186.65   10.117%   $205.5334   $205.53   $205.55   $205.50  
  Purchase #2 $96.73   9.135%   $105.5663   $105.57   $105.55   $105.60  
  Purchase #3 $192.99   6.826%   $206.1635   $206.16   $206.15   $206.20  
  Purchase #4 $212.52   9.347%   $232.3842   $232.38   $232.40   $232.40  
  Purchase #5 $121.37   5.200%   $127.6812   $127.68   $127.70   $127.70  
  Purchase #6 $177.51   6.723%   $189.444   $189.44   $189.45   $189.40  
  Purchase #7 $249.85   6.259%   $265.4881   $265.49   $265.50   $265.50  
  7 purchase totals = $1,237.62       $1,332.2607   $1,332.25   $1,332.30   $1,332.30