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 $222.84   11.314%   $248.0521   $248.05   $248.05   $248.10  
  Purchase #2 $50.89   3.668%   $52.7566   $52.76   $52.75   $52.80  
  Purchase #3 $55.68   8.627%   $60.4835   $60.48   $60.50   $60.50  
  Purchase #4 $57.72   7.339%   $61.9561   $61.96   $61.95   $62.00  
  Purchase #5 $151.88   13.809%   $172.8531   $172.85   $172.85   $172.90  
  Purchase #6 $127.87   6.750%   $136.5012   $136.50   $136.50   $136.50  
  Purchase #7 $201.51   11.641%   $224.9678   $224.97   $224.95   $225.00  
  7 purchase totals = $868.39       $957.5704   $957.57   $957.55   $957.80