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 $55.99   6.467%   $59.6109   $59.61   $59.60   $59.60  
  Purchase #2 $176.97   5.229%   $186.2238   $186.22   $186.20   $186.20  
  Purchase #3 $101.60   9.295%   $111.0437   $111.04   $111.05   $111.00  
  Purchase #4 $215.60   5.115%   $226.6279   $226.63   $226.65   $226.60  
  Purchase #5 $227.70   5.868%   $241.0614   $241.06   $241.05   $241.10  
  Purchase #6 $55.30   6.633%   $58.968   $58.97   $58.95   $59.00  
  Purchase #7 $90.73   8.647%   $98.5754   $98.58   $98.60   $98.60  
  7 purchase totals = $923.89       $982.1111   $982.11   $982.10   $982.10