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 $186.39   10.656%   $206.2517   $206.25   $206.25   $206.30  
  Purchase #2 $224.59   13.345%   $254.5615   $254.56   $254.55   $254.60  
  Purchase #3 $176.32   6.281%   $187.3947   $187.39   $187.40   $187.40  
  Purchase #4 $164.63   11.300%   $183.2332   $183.23   $183.25   $183.20  
  Purchase #5 $52.82   11.114%   $58.6904   $58.69   $58.70   $58.70  
  Purchase #6 $153.40   11.295%   $170.7265   $170.73   $170.75   $170.70  
  Purchase #7 $12.82   9.854%   $14.0833   $14.08   $14.10   $14.10  
  7 purchase totals = $970.97       $1,074.9413   $1,074.93   $1,075.00   $1,075.00