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 $53.98   12.343%   $60.6428   $60.64   $60.65   $60.60  
  Purchase #2 $146.59   12.118%   $164.3538   $164.35   $164.35   $164.40  
  Purchase #3 $211.65   13.190%   $239.5666   $239.57   $239.55   $239.60  
  Purchase #4 $115.40   8.364%   $125.0521   $125.05   $125.05   $125.10  
  Purchase #5 $187.76   12.367%   $210.9803   $210.98   $211.00   $211.00  
  Purchase #6 $14.57   9.267%   $15.9202   $15.92   $15.90   $15.90  
  Purchase #7 $49.98   12.533%   $56.244   $56.24   $56.25   $56.20  
  7 purchase totals = $779.93       $872.7598   $872.75   $872.75   $872.80