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 $214.75   10.165%   $236.5793   $236.58   $236.60   $236.60  
  Purchase #2 $77.37   3.322%   $79.9402   $79.94   $79.95   $79.90  
  Purchase #3 $179.99   8.516%   $195.3179   $195.32   $195.30   $195.30  
  Purchase #4 $54.40   7.811%   $58.6492   $58.65   $58.65   $58.60  
  Purchase #5 $154.36   10.161%   $170.0445   $170.04   $170.05   $170.00  
  Purchase #6 $221.76   5.710%   $234.4225   $234.42   $234.40   $234.40  
  Purchase #7 $49.42   7.386%   $53.0702   $53.07   $53.05   $53.10  
  7 purchase totals = $952.05       $1,028.0238   $1,028.02   $1,028.00   $1,027.90