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 $194.69   6.180%   $206.7218   $206.72   $206.70   $206.70  
  Purchase #2 $241.56   13.804%   $274.9049   $274.90   $274.90   $274.90  
  Purchase #3 $68.26   3.509%   $70.6552   $70.66   $70.65   $70.70  
  Purchase #4 $61.81   9.182%   $67.4854   $67.49   $67.50   $67.50  
  Purchase #5 $168.77   5.453%   $177.973   $177.97   $177.95   $178.00  
  Purchase #6 $173.74   12.272%   $195.0614   $195.06   $195.05   $195.10  
  Purchase #7 $12.87   8.609%   $13.978   $13.98   $14.00   $14.00  
  7 purchase totals = $921.70       $1,006.7797   $1,006.78   $1,006.75   $1,006.90