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 $180.56   9.212%   $197.1932   $197.19   $197.20   $197.20  
  Purchase #2 $36.81   12.108%   $41.267   $41.27   $41.25   $41.30  
  Purchase #3 $160.33   4.135%   $166.9596   $166.96   $166.95   $167.00  
  Purchase #4 $66.71   5.653%   $70.4811   $70.48   $70.50   $70.50  
  Purchase #5 $179.72   12.446%   $202.088   $202.09   $202.10   $202.10  
  Purchase #6 $82.35   7.605%   $88.6127   $88.61   $88.60   $88.60  
  Purchase #7 $79.46   9.213%   $86.7806   $86.78   $86.80   $86.80  
  7 purchase totals = $785.94       $853.3822   $853.38   $853.40   $853.50