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 $49.41   7.160%   $52.9478   $52.95   $52.95   $52.90  
  Purchase #2 $214.51   9.587%   $235.0751   $235.08   $235.10   $235.10  
  Purchase #3 $218.58   12.526%   $245.9593   $245.96   $245.95   $246.00  
  Purchase #4 $248.56   10.188%   $273.8833   $273.88   $273.90   $273.90  
  Purchase #5 $125.63   13.857%   $143.0385   $143.04   $143.05   $143.00  
  Purchase #6 $116.51   7.403%   $125.1352   $125.14   $125.15   $125.10  
  Purchase #7 $119.80   8.856%   $130.4095   $130.41   $130.40   $130.40  
  7 purchase totals = $1,093.00       $1,206.4487   $1,206.46   $1,206.50   $1,206.40