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 $206.59   13.729%   $234.9527   $234.95   $234.95   $235.00  
  Purchase #2 $129.74   13.339%   $147.046   $147.05   $147.05   $147.00  
  Purchase #3 $76.98   11.139%   $85.5548   $85.55   $85.55   $85.60  
  Purchase #4 $116.81   8.812%   $127.1033   $127.10   $127.10   $127.10  
  Purchase #5 $75.66   13.732%   $86.0496   $86.05   $86.05   $86.00  
  Purchase #6 $92.85   10.219%   $102.3383   $102.34   $102.35   $102.30  
  Purchase #7 $25.45   4.659%   $26.6357   $26.64   $26.65   $26.60  
  7 purchase totals = $724.08       $809.6804   $809.68   $809.70   $809.60