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 $187.67   9.812%   $206.0842   $206.08   $206.10   $206.10  
  Purchase #2 $96.87   7.164%   $103.8098   $103.81   $103.80   $103.80  
  Purchase #3 $135.31   3.291%   $139.7631   $139.76   $139.75   $139.80  
  Purchase #4 $168.89   13.103%   $191.0197   $191.02   $191.00   $191.00  
  Purchase #5 $112.81   8.628%   $122.5432   $122.54   $122.55   $122.50  
  Purchase #6 $169.30   4.231%   $176.4631   $176.46   $176.45   $176.50  
  Purchase #7 $82.59   4.763%   $86.5238   $86.52   $86.50   $86.50  
  7 purchase totals = $953.44       $1,026.2069   $1,026.19   $1,026.15   $1,026.20