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 $62.38   4.618%   $65.2607   $65.26   $65.25   $65.30  
  Purchase #2 $183.87   8.523%   $199.5412   $199.54   $199.55   $199.50  
  Purchase #3 $197.50   5.844%   $209.0419   $209.04   $209.05   $209.00  
  Purchase #4 $52.78   8.697%   $57.3703   $57.37   $57.35   $57.40  
  Purchase #5 $109.94   4.138%   $114.4893   $114.49   $114.50   $114.50  
  Purchase #6 $26.94   9.516%   $29.5036   $29.50   $29.50   $29.50  
  Purchase #7 $144.62   11.160%   $160.7596   $160.76   $160.75   $160.80  
  7 purchase totals = $778.03       $835.9666   $835.96   $835.95   $836.00