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 $61.37   12.727%   $69.1806   $69.18   $69.20   $69.20  
  Purchase #2 $25.63   13.295%   $29.0375   $29.04   $29.05   $29.00  
  Purchase #3 $36.34   8.807%   $39.5405   $39.54   $39.55   $39.50  
  Purchase #4 $124.82   6.782%   $133.2853   $133.29   $133.30   $133.30  
  Purchase #5 $170.34   7.571%   $183.2364   $183.24   $183.25   $183.20  
  Purchase #6 $241.45   11.552%   $269.3423   $269.34   $269.35   $269.30  
  Purchase #7 $198.39   5.278%   $208.861   $208.86   $208.85   $208.90  
  7 purchase totals = $858.34       $932.4836   $932.49   $932.55   $932.40