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 $239.27   12.410%   $268.9634   $268.96   $268.95   $269.00  
  Purchase #2 $117.45   8.179%   $127.0562   $127.06   $127.05   $127.10  
  Purchase #3 $50.68   10.322%   $55.9112   $55.91   $55.90   $55.90  
  Purchase #4 $232.94   13.761%   $264.9949   $264.99   $265.00   $265.00  
  Purchase #5 $150.67   4.259%   $157.087   $157.09   $157.10   $157.10  
  Purchase #6 $151.59   7.707%   $163.273   $163.27   $163.25   $163.30  
  Purchase #7 $53.90   13.742%   $61.3069   $61.31   $61.30   $61.30  
  7 purchase totals = $996.50       $1,098.5926   $1,098.59   $1,098.55   $1,098.70