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 $147.67   3.123%   $152.2817   $152.28   $152.30   $152.30  
  Purchase #2 $225.79   11.854%   $252.5551   $252.56   $252.55   $252.60  
  Purchase #3 $187.80   13.797%   $213.7108   $213.71   $213.70   $213.70  
  Purchase #4 $207.73   8.214%   $224.7929   $224.79   $224.80   $224.80  
  Purchase #5 $103.64   9.648%   $113.6392   $113.64   $113.65   $113.60  
  Purchase #6 $125.36   8.619%   $136.1648   $136.16   $136.15   $136.20  
  Purchase #7 $24.69   7.773%   $26.6092   $26.61   $26.60   $26.60  
  7 purchase totals = $1,022.68       $1,119.7537   $1,119.75   $1,119.75   $1,119.80