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 $226.61   12.794%   $255.6025   $255.60   $255.60   $255.60  
  Purchase #2 $146.63   10.433%   $161.9279   $161.93   $161.95   $161.90  
  Purchase #3 $179.25   5.181%   $188.5369   $188.54   $188.55   $188.50  
  Purchase #4 $77.99   10.345%   $86.0581   $86.06   $86.05   $86.10  
  Purchase #5 $109.86   6.227%   $116.701   $116.70   $116.70   $116.70  
  Purchase #6 $111.34   5.273%   $117.211   $117.21   $117.20   $117.20  
  Purchase #7 $97.25   9.331%   $106.3244   $106.32   $106.30   $106.30  
  7 purchase totals = $948.93       $1,032.3618   $1,032.36   $1,032.35   $1,032.30