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 $54.63   13.711%   $62.1203   $62.12   $62.10   $62.10  
  Purchase #2 $208.82   11.248%   $232.3081   $232.31   $232.30   $232.30  
  Purchase #3 $85.25   11.602%   $95.1407   $95.14   $95.15   $95.10  
  Purchase #4 $44.73   6.824%   $47.7824   $47.78   $47.80   $47.80  
  Purchase #5 $10.92   12.352%   $12.2688   $12.27   $12.25   $12.30  
  Purchase #6 $113.42   8.423%   $122.9734   $122.97   $122.95   $123.00  
  Purchase #7 $233.70   6.749%   $249.4724   $249.47   $249.45   $249.50  
  7 purchase totals = $751.47       $822.0661   $822.06   $822.00   $822.10