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 $42.91   13.469%   $48.6895   $48.69   $48.70   $48.70  
  Purchase #2 $136.56   12.773%   $154.0028   $154.00   $154.00   $154.00  
  Purchase #3 $219.58   12.493%   $247.0121   $247.01   $247.00   $247.00  
  Purchase #4 $235.41   10.861%   $260.9779   $260.98   $261.00   $261.00  
  Purchase #5 $76.57   13.295%   $86.75   $86.75   $86.75   $86.80  
  Purchase #6 $191.46   12.449%   $215.2949   $215.29   $215.30   $215.30  
  Purchase #7 $166.68   9.745%   $182.923   $182.92   $182.90   $182.90  
  7 purchase totals = $1,069.17       $1,195.6502   $1,195.64   $1,195.65   $1,195.70