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 $139.33   13.432%   $158.0448   $158.04   $158.05   $158.00  
  Purchase #2 $136.55   5.458%   $144.0029   $144.00   $144.00   $144.00  
  Purchase #3 $28.33   3.301%   $29.2652   $29.27   $29.25   $29.30  
  Purchase #4 $177.45   4.557%   $185.5364   $185.54   $185.55   $185.50  
  Purchase #5 $227.38   12.131%   $254.9635   $254.96   $254.95   $255.00  
  Purchase #6 $203.67   6.394%   $216.6927   $216.69   $216.70   $216.70  
  Purchase #7 $33.46   12.535%   $37.6542   $37.65   $37.65   $37.70  
  7 purchase totals = $946.17       $1,026.1597   $1,026.15   $1,026.15   $1,026.20