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 $206.52   8.497%   $224.068   $224.07   $224.05   $224.10  
  Purchase #2 $71.69   3.587%   $74.2615   $74.26   $74.25   $74.30  
  Purchase #3 $76.58   4.742%   $80.2114   $80.21   $80.20   $80.20  
  Purchase #4 $79.57   8.858%   $86.6183   $86.62   $86.60   $86.60  
  Purchase #5 $89.72   5.368%   $94.5362   $94.54   $94.55   $94.50  
  Purchase #6 $25.30   3.592%   $26.2088   $26.21   $26.20   $26.20  
  Purchase #7 $218.88   11.281%   $243.5719   $243.57   $243.55   $243.60  
  7 purchase totals = $768.26       $829.4761   $829.48   $829.40   $829.50