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 $54.83   12.270%   $61.5576   $61.56   $61.55   $61.60  
  Purchase #2 $104.37   8.504%   $113.2456   $113.25   $113.25   $113.20  
  Purchase #3 $215.64   5.410%   $227.3061   $227.31   $227.30   $227.30  
  Purchase #4 $147.41   4.626%   $154.2292   $154.23   $154.25   $154.20  
  Purchase #5 $172.28   6.286%   $183.1095   $183.11   $183.10   $183.10  
  Purchase #6 $15.74   11.200%   $17.5029   $17.50   $17.50   $17.50  
  Purchase #7 $53.76   9.856%   $59.0586   $59.06   $59.05   $59.10  
  7 purchase totals = $764.03       $816.0095   $816.02   $816.00   $816.00