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 $191.31   9.216%   $208.9411   $208.94   $208.95   $208.90  
  Purchase #2 $122.73   11.310%   $136.6108   $136.61   $136.60   $136.60  
  Purchase #3 $73.78   11.361%   $82.1621   $82.16   $82.15   $82.20  
  Purchase #4 $77.58   13.214%   $87.8314   $87.83   $87.85   $87.80  
  Purchase #5 $167.80   11.226%   $186.6372   $186.64   $186.65   $186.60  
  Purchase #6 $162.60   7.661%   $175.0568   $175.06   $175.05   $175.10  
  Purchase #7 $80.93   6.360%   $86.0771   $86.08   $86.10   $86.10  
  7 purchase totals = $876.73       $963.3165   $963.32   $963.35   $963.30