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 $105.26   12.524%   $118.4428   $118.44   $118.45   $118.40  
  Purchase #2 $117.39   4.413%   $122.5704   $122.57   $122.55   $122.60  
  Purchase #3 $154.52   5.658%   $163.2627   $163.26   $163.25   $163.30  
  Purchase #4 $223.86   4.344%   $233.5845   $233.58   $233.60   $233.60  
  Purchase #5 $176.62   11.653%   $197.2015   $197.20   $197.20   $197.20  
  Purchase #6 $54.76   3.398%   $56.6207   $56.62   $56.60   $56.60  
  Purchase #7 $84.42   12.441%   $94.9227   $94.92   $94.90   $94.90  
  7 purchase totals = $916.83       $986.6053   $986.59   $986.55   $986.60