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 $37.42   11.423%   $41.6945   $41.69   $41.70   $41.70  
  Purchase #2 $5.59   8.184%   $6.0475   $6.05   $6.05   $6.00  
  Purchase #3 $29.37   10.723%   $32.5193   $32.52   $32.50   $32.50  
  Purchase #4 $57.36   9.854%   $63.0123   $63.01   $63.00   $63.00  
  Purchase #5 $229.64   8.487%   $249.1295   $249.13   $249.15   $249.10  
  Purchase #6 $114.75   8.532%   $124.5405   $124.54   $124.55   $124.50  
  Purchase #7 $96.70   11.839%   $108.1483   $108.15   $108.15   $108.10  
  7 purchase totals = $570.83       $625.0919   $625.09   $625.10   $624.90