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 $86.32   6.549%   $91.9731   $91.97   $91.95   $92.00  
  Purchase #2 $238.66   9.587%   $261.5403   $261.54   $261.55   $261.50  
  Purchase #3 $26.96   12.437%   $30.313   $30.31   $30.30   $30.30  
  Purchase #4 $164.86   10.406%   $182.0153   $182.02   $182.00   $182.00  
  Purchase #5 $141.69   9.536%   $155.2016   $155.20   $155.20   $155.20  
  Purchase #6 $232.72   13.259%   $263.5763   $263.58   $263.60   $263.60  
  Purchase #7 $173.51   3.683%   $179.9004   $179.90   $179.90   $179.90  
  7 purchase totals = $1,064.72       $1,164.5200   $1,164.52   $1,164.50   $1,164.50