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 $49.63   13.529%   $56.3444   $56.34   $56.35   $56.30  
  Purchase #2 $103.38   13.121%   $116.9445   $116.94   $116.95   $116.90  
  Purchase #3 $71.88   13.491%   $81.5773   $81.58   $81.60   $81.60  
  Purchase #4 $57.47   6.239%   $61.0556   $61.06   $61.05   $61.10  
  Purchase #5 $226.61   7.267%   $243.0777   $243.08   $243.10   $243.10  
  Purchase #6 $212.66   10.479%   $234.9446   $234.94   $234.95   $234.90  
  Purchase #7 $68.81   9.394%   $75.274   $75.27   $75.25   $75.30  
  7 purchase totals = $790.44       $869.2181   $869.21   $869.25   $869.20