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 $89.50   6.794%   $95.5806   $95.58   $95.60   $95.60  
  Purchase #2 $168.37   8.596%   $182.8431   $182.84   $182.85   $182.80  
  Purchase #3 $6.54   3.712%   $6.7828   $6.78   $6.80   $6.80  
  Purchase #4 $103.69   7.199%   $111.1546   $111.15   $111.15   $111.20  
  Purchase #5 $82.89   4.713%   $86.7966   $86.80   $86.80   $86.80  
  Purchase #6 $162.99   9.204%   $177.9916   $177.99   $178.00   $178.00  
  Purchase #7 $102.27   12.493%   $115.0466   $115.05   $115.05   $115.00  
  7 purchase totals = $716.25       $776.1959   $776.19   $776.25   $776.20