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 $208.93   8.757%   $227.226   $227.23   $227.25   $227.20  
  Purchase #2 $155.44   7.313%   $166.8073   $166.81   $166.80   $166.80  
  Purchase #3 $198.52   4.600%   $207.6519   $207.65   $207.65   $207.70  
  Purchase #4 $121.90   10.367%   $134.5374   $134.54   $134.55   $134.50  
  Purchase #5 $39.27   10.204%   $43.2771   $43.28   $43.30   $43.30  
  Purchase #6 $139.42   10.466%   $154.0117   $154.01   $154.00   $154.00  
  Purchase #7 $81.67   11.262%   $90.8677   $90.87   $90.85   $90.90  
  7 purchase totals = $945.15       $1,024.3791   $1,024.39   $1,024.40   $1,024.40