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 $195.69   10.866%   $216.9537   $216.95   $216.95   $217.00  
  Purchase #2 $201.53   13.400%   $228.535   $228.54   $228.55   $228.50  
  Purchase #3 $127.81   7.201%   $137.0136   $137.01   $137.00   $137.00  
  Purchase #4 $199.85   6.322%   $212.4845   $212.48   $212.50   $212.50  
  Purchase #5 $48.71   3.221%   $50.2789   $50.28   $50.30   $50.30  
  Purchase #6 $237.70   11.765%   $265.6654   $265.67   $265.65   $265.70  
  Purchase #7 $46.30   5.613%   $48.8988   $48.90   $48.90   $48.90  
  7 purchase totals = $1,057.59       $1,159.8299   $1,159.83   $1,159.85   $1,159.90