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 $61.81   8.389%   $66.9952   $67.00   $67.00   $67.00  
  Purchase #2 $124.25   5.448%   $131.0191   $131.02   $131.00   $131.00  
  Purchase #3 $136.93   7.170%   $146.7479   $146.75   $146.75   $146.70  
  Purchase #4 $248.80   13.620%   $282.6866   $282.69   $282.70   $282.70  
  Purchase #5 $97.40   6.162%   $103.4018   $103.40   $103.40   $103.40  
  Purchase #6 $18.61   11.542%   $20.758   $20.76   $20.75   $20.80  
  Purchase #7 $96.64   11.652%   $107.9005   $107.90   $107.90   $107.90  
  7 purchase totals = $784.44       $859.5091   $859.52   $859.50   $859.50