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 $175.58   9.593%   $192.4234   $192.42   $192.40   $192.40  
  Purchase #2 $235.59   10.226%   $259.6814   $259.68   $259.70   $259.70  
  Purchase #3 $174.26   11.523%   $194.34   $194.34   $194.35   $194.30  
  Purchase #4 $183.63   10.114%   $202.2023   $202.20   $202.20   $202.20  
  Purchase #5 $184.60   12.740%   $208.118   $208.12   $208.10   $208.10  
  Purchase #6 $52.28   3.278%   $53.9937   $53.99   $54.00   $54.00  
  Purchase #7 $125.40   11.527%   $139.8549   $139.85   $139.85   $139.90  
  7 purchase totals = $1,131.34       $1,250.6137   $1,250.60   $1,250.60   $1,250.60