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 $77.64   11.303%   $86.4156   $86.42   $86.40   $86.40  
  Purchase #2 $190.53   9.192%   $208.0435   $208.04   $208.05   $208.00  
  Purchase #3 $93.53   4.383%   $97.6294   $97.63   $97.65   $97.60  
  Purchase #4 $77.40   8.390%   $83.8939   $83.89   $83.90   $83.90  
  Purchase #5 $110.64   13.567%   $125.6505   $125.65   $125.65   $125.70  
  Purchase #6 $243.27   12.202%   $272.9538   $272.95   $272.95   $273.00  
  Purchase #7 $146.39   3.523%   $151.5473   $151.55   $151.55   $151.50  
  7 purchase totals = $939.40       $1,026.1340   $1,026.13   $1,026.15   $1,026.10