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 $60.53   11.750%   $67.6423   $67.64   $67.65   $67.60  
  Purchase #2 $241.61   4.591%   $252.7023   $252.70   $252.70   $252.70  
  Purchase #3 $137.27   9.269%   $149.9936   $149.99   $150.00   $150.00  
  Purchase #4 $71.88   13.659%   $81.6981   $81.70   $81.70   $81.70  
  Purchase #5 $110.53   11.816%   $123.5902   $123.59   $123.60   $123.60  
  Purchase #6 $242.89   4.571%   $253.9925   $253.99   $254.00   $254.00  
  Purchase #7 $26.64   3.228%   $27.4999   $27.50   $27.50   $27.50  
  7 purchase totals = $891.35       $957.1189   $957.11   $957.15   $957.10