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 $61.51   12.593%   $69.256   $69.26   $69.25   $69.30  
  Purchase #2 $168.46   12.688%   $189.8342   $189.83   $189.85   $189.80  
  Purchase #3 $72.90   13.389%   $82.6606   $82.66   $82.65   $82.70  
  Purchase #4 $239.97   3.822%   $249.1417   $249.14   $249.15   $249.10  
  Purchase #5 $29.84   12.270%   $33.5014   $33.50   $33.50   $33.50  
  Purchase #6 $116.49   7.127%   $124.7922   $124.79   $124.80   $124.80  
  Purchase #7 $218.45   3.866%   $226.8953   $226.90   $226.90   $226.90  
  7 purchase totals = $907.62       $976.0814   $976.08   $976.10   $976.10