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 $218.57   3.670%   $226.5915   $226.59   $226.60   $226.60  
  Purchase #2 $220.82   6.722%   $235.6635   $235.66   $235.65   $235.70  
  Purchase #3 $214.36   4.713%   $224.4628   $224.46   $224.45   $224.50  
  Purchase #4 $72.68   13.816%   $82.7215   $82.72   $82.70   $82.70  
  Purchase #5 $207.71   7.179%   $222.6215   $222.62   $222.60   $222.60  
  Purchase #6 $137.63   11.195%   $153.0377   $153.04   $153.05   $153.00  
  Purchase #7 $202.90   8.138%   $219.412   $219.41   $219.40   $219.40  
  7 purchase totals = $1,274.67       $1,364.5105   $1,364.50   $1,364.45   $1,364.50