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 $146.40   7.399%   $157.2321   $157.23   $157.25   $157.20  
  Purchase #2 $175.79   12.826%   $198.3368   $198.34   $198.35   $198.30  
  Purchase #3 $23.77   9.553%   $26.0407   $26.04   $26.05   $26.00  
  Purchase #4 $128.92   11.547%   $143.8064   $143.81   $143.80   $143.80  
  Purchase #5 $236.63   8.144%   $255.9011   $255.90   $255.90   $255.90  
  Purchase #6 $238.43   11.795%   $266.5528   $266.55   $266.55   $266.60  
  Purchase #7 $5.97   7.495%   $6.4175   $6.42   $6.40   $6.40  
  7 purchase totals = $955.91       $1,054.2874   $1,054.29   $1,054.30   $1,054.20