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 $179.80   5.345%   $189.4103   $189.41   $189.40   $189.40  
  Purchase #2 $116.28   9.150%   $126.9196   $126.92   $126.90   $126.90  
  Purchase #3 $129.51   8.137%   $140.0482   $140.05   $140.05   $140.00  
  Purchase #4 $77.63   13.661%   $88.235   $88.24   $88.25   $88.20  
  Purchase #5 $69.33   5.835%   $73.3754   $73.38   $73.40   $73.40  
  Purchase #6 $83.86   4.222%   $87.4006   $87.40   $87.40   $87.40  
  Purchase #7 $206.48   3.868%   $214.4666   $214.47   $214.45   $214.50  
  7 purchase totals = $862.89       $919.8557   $919.87   $919.85   $919.80