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 $239.66   13.293%   $271.518   $271.52   $271.50   $271.50  
  Purchase #2 $249.35   4.241%   $259.9249   $259.92   $259.90   $259.90  
  Purchase #3 $114.78   7.762%   $123.6892   $123.69   $123.70   $123.70  
  Purchase #4 $64.30   9.801%   $70.602   $70.60   $70.60   $70.60  
  Purchase #5 $197.51   7.715%   $212.7479   $212.75   $212.75   $212.70  
  Purchase #6 $169.76   9.525%   $185.9296   $185.93   $185.95   $185.90  
  Purchase #7 $64.51   5.641%   $68.149   $68.15   $68.15   $68.10  
  7 purchase totals = $1,099.87       $1,192.5606   $1,192.56   $1,192.55   $1,192.40