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 $67.60   5.826%   $71.5384   $71.54   $71.55   $71.50  
  Purchase #2 $91.58   3.128%   $94.4446   $94.44   $94.45   $94.40  
  Purchase #3 $167.28   9.441%   $183.0729   $183.07   $183.05   $183.10  
  Purchase #4 $161.64   5.634%   $170.7468   $170.75   $170.75   $170.70  
  Purchase #5 $81.48   6.289%   $86.6043   $86.60   $86.60   $86.60  
  Purchase #6 $98.98   11.337%   $110.2014   $110.20   $110.20   $110.20  
  Purchase #7 $192.93   8.274%   $208.893   $208.89   $208.90   $208.90  
  7 purchase totals = $861.49       $925.5014   $925.49   $925.50   $925.40