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 $171.93   8.279%   $186.1641   $186.16   $186.15   $186.20  
  Purchase #2 $243.70   12.597%   $274.3989   $274.40   $274.40   $274.40  
  Purchase #3 $53.92   5.758%   $57.0247   $57.02   $57.00   $57.00  
  Purchase #4 $14.71   13.563%   $16.7051   $16.71   $16.70   $16.70  
  Purchase #5 $77.30   6.113%   $82.0253   $82.03   $82.05   $82.00  
  Purchase #6 $232.99   8.572%   $252.9619   $252.96   $252.95   $253.00  
  Purchase #7 $138.85   6.105%   $147.3268   $147.33   $147.35   $147.30  
  7 purchase totals = $933.40       $1,016.6068   $1,016.61   $1,016.60   $1,016.60