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 $182.32   8.496%   $197.8099   $197.81   $197.80   $197.80  
  Purchase #2 $192.26   7.163%   $206.0316   $206.03   $206.05   $206.00  
  Purchase #3 $233.30   7.584%   $250.9935   $250.99   $251.00   $251.00  
  Purchase #4 $117.52   7.818%   $126.7077   $126.71   $126.70   $126.70  
  Purchase #5 $97.88   5.680%   $103.4396   $103.44   $103.45   $103.40  
  Purchase #6 $108.25   5.680%   $114.3986   $114.40   $114.40   $114.40  
  Purchase #7 $211.37   12.228%   $237.2163   $237.22   $237.20   $237.20  
  7 purchase totals = $1,142.90       $1,236.5972   $1,236.60   $1,236.60   $1,236.50