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 $79.41   5.501%   $83.7783   $83.78   $83.80   $83.80  
  Purchase #2 $5.50   11.144%   $6.1129   $6.11   $6.10   $6.10  
  Purchase #3 $148.95   5.193%   $156.685   $156.69   $156.70   $156.70  
  Purchase #4 $207.81   3.846%   $215.8024   $215.80   $215.80   $215.80  
  Purchase #5 $183.96   4.680%   $192.5693   $192.57   $192.55   $192.60  
  Purchase #6 $118.92   13.240%   $134.665   $134.67   $134.65   $134.70  
  Purchase #7 $250.43   6.489%   $266.6804   $266.68   $266.70   $266.70  
  7 purchase totals = $994.98       $1,056.2933   $1,056.30   $1,056.30   $1,056.40