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 $86.44   7.188%   $92.6533   $92.65   $92.65   $92.70  
  Purchase #2 $182.85   8.672%   $198.7068   $198.71   $198.70   $198.70  
  Purchase #3 $171.68   4.553%   $179.4966   $179.50   $179.50   $179.50  
  Purchase #4 $36.93   13.474%   $41.9059   $41.91   $41.90   $41.90  
  Purchase #5 $208.41   5.118%   $219.0764   $219.08   $219.10   $219.10  
  Purchase #6 $168.59   4.697%   $176.5087   $176.51   $176.50   $176.50  
  Purchase #7 $177.76   12.752%   $200.428   $200.43   $200.45   $200.40  
  7 purchase totals = $1,032.66       $1,108.7757   $1,108.79   $1,108.80   $1,108.80