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 $74.81   8.392%   $81.0881   $81.09   $81.10   $81.10  
  Purchase #2 $186.29   13.382%   $211.2193   $211.22   $211.20   $211.20  
  Purchase #3 $226.43   8.411%   $245.475   $245.48   $245.50   $245.50  
  Purchase #4 $82.91   10.577%   $91.6794   $91.68   $91.70   $91.70  
  Purchase #5 $118.43   5.204%   $124.5931   $124.59   $124.60   $124.60  
  Purchase #6 $49.98   7.267%   $53.612   $53.61   $53.60   $53.60  
  Purchase #7 $242.26   4.269%   $252.6021   $252.60   $252.60   $252.60  
  7 purchase totals = $981.11       $1,060.2690   $1,060.27   $1,060.30   $1,060.30