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 $60.93   9.863%   $66.9395   $66.94   $66.95   $66.90  
  Purchase #2 $226.84   5.594%   $239.5294   $239.53   $239.55   $239.50  
  Purchase #3 $163.42   10.866%   $181.1772   $181.18   $181.20   $181.20  
  Purchase #4 $165.57   7.198%   $177.4877   $177.49   $177.50   $177.50  
  Purchase #5 $193.43   9.795%   $212.3765   $212.38   $212.40   $212.40  
  Purchase #6 $101.28   12.828%   $114.2722   $114.27   $114.25   $114.30  
  Purchase #7 $180.62   11.367%   $201.1511   $201.15   $201.15   $201.20  
  7 purchase totals = $1,092.09       $1,192.9336   $1,192.94   $1,193.00   $1,193.00