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 $112.36   9.211%   $122.7095   $122.71   $122.70   $122.70  
  Purchase #2 $98.40   6.792%   $105.0833   $105.08   $105.10   $105.10  
  Purchase #3 $101.70   10.443%   $112.3205   $112.32   $112.30   $112.30  
  Purchase #4 $193.35   4.737%   $202.509   $202.51   $202.50   $202.50  
  Purchase #5 $62.62   13.217%   $70.8965   $70.90   $70.90   $70.90  
  Purchase #6 $215.98   3.230%   $222.9562   $222.96   $222.95   $223.00  
  Purchase #7 $184.92   12.483%   $208.0036   $208.00   $208.00   $208.00  
  7 purchase totals = $969.33       $1,044.4786   $1,044.48   $1,044.45   $1,044.50