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 $166.59   8.785%   $181.2249   $181.22   $181.20   $181.20  
  Purchase #2 $248.45   4.233%   $258.9669   $258.97   $258.95   $259.00  
  Purchase #3 $89.26   4.519%   $93.2937   $93.29   $93.30   $93.30  
  Purchase #4 $53.39   9.868%   $58.6585   $58.66   $58.65   $58.70  
  Purchase #5 $69.82   9.584%   $76.5115   $76.51   $76.50   $76.50  
  Purchase #6 $82.54   9.664%   $90.5167   $90.52   $90.50   $90.50  
  Purchase #7 $60.55   10.537%   $66.9302   $66.93   $66.95   $66.90  
  7 purchase totals = $770.60       $826.1024   $826.10   $826.05   $826.10