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 $24.84   6.233%   $26.3883   $26.39   $26.40   $26.40  
  Purchase #2 $190.80   6.693%   $203.5702   $203.57   $203.55   $203.60  
  Purchase #3 $205.47   9.589%   $225.1725   $225.17   $225.15   $225.20  
  Purchase #4 $98.87   4.316%   $103.1372   $103.14   $103.15   $103.10  
  Purchase #5 $61.54   5.123%   $64.6927   $64.69   $64.70   $64.70  
  Purchase #6 $111.80   10.601%   $123.6519   $123.65   $123.65   $123.70  
  Purchase #7 $237.82   10.778%   $263.4522   $263.45   $263.45   $263.50  
  7 purchase totals = $931.14       $1,010.0650   $1,010.06   $1,010.05   $1,010.20