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 $59.74   3.679%   $61.9378   $61.94   $61.95   $61.90  
  Purchase #2 $163.42   5.670%   $172.6859   $172.69   $172.70   $172.70  
  Purchase #3 $91.96   7.127%   $98.514   $98.51   $98.50   $98.50  
  Purchase #4 $200.94   12.866%   $226.7929   $226.79   $226.80   $226.80  
  Purchase #5 $22.25   7.864%   $23.9997   $24.00   $24.00   $24.00  
  Purchase #6 $235.25   9.204%   $256.9024   $256.90   $256.90   $256.90  
  Purchase #7 $128.54   11.874%   $143.8028   $143.80   $143.80   $143.80  
  7 purchase totals = $902.10       $984.6355   $984.63   $984.65   $984.60