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 $226.63   8.522%   $245.9434   $245.94   $245.95   $245.90  
  Purchase #2 $204.63   3.387%   $211.5608   $211.56   $211.55   $211.60  
  Purchase #3 $84.44   8.802%   $91.8724   $91.87   $91.85   $91.90  
  Purchase #4 $179.32   9.512%   $196.3769   $196.38   $196.40   $196.40  
  Purchase #5 $105.26   8.725%   $114.4439   $114.44   $114.45   $114.40  
  Purchase #6 $65.65   8.295%   $71.0957   $71.10   $71.10   $71.10  
  Purchase #7 $6.52   7.257%   $6.9932   $6.99   $7.00   $7.00  
  7 purchase totals = $872.45       $938.2863   $938.28   $938.30   $938.30